1 /*
2 * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.misc.JavaLangAccess;
29 import jdk.internal.misc.SharedSecrets;
30 import jdk.internal.module.IllegalAccessLogger;
31 import jdk.internal.org.objectweb.asm.ClassReader;
32 import jdk.internal.reflect.CallerSensitive;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.vm.annotation.ForceInline;
35 import sun.invoke.util.ValueConversions;
36 import sun.invoke.util.VerifyAccess;
37 import sun.invoke.util.Wrapper;
38 import sun.reflect.misc.ReflectUtil;
39 import sun.security.util.SecurityConstants;
40
41 import java.lang.invoke.LambdaForm.BasicType;
42 import java.lang.reflect.Constructor;
43 import java.lang.reflect.Field;
44 import java.lang.reflect.Member;
45 import java.lang.reflect.Method;
46 import java.lang.reflect.Modifier;
47 import java.lang.reflect.ReflectPermission;
48 import java.nio.ByteOrder;
49 import java.security.ProtectionDomain;
50 import java.util.ArrayList;
51 import java.util.Arrays;
52 import java.util.BitSet;
53 import java.util.Iterator;
54 import java.util.List;
55 import java.util.Objects;
56 import java.util.Set;
57 import java.util.WeakHashMap;
58 import java.util.concurrent.ConcurrentHashMap;
59 import java.util.stream.Collectors;
60 import java.util.stream.Stream;
61
62 import static java.lang.invoke.MethodHandles.Lookup.ClassProperty.*;
63 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
64 import static java.lang.invoke.MethodHandleNatives.Constants.*;
65 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
66 import static java.lang.invoke.MethodType.methodType;
67
68 /**
69 * This class consists exclusively of static methods that operate on or return
70 * method handles. They fall into several categories:
71 * <ul>
72 * <li>Lookup methods which help create method handles for methods and fields.
73 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
74 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
75 * </ul>
76 * A lookup, combinator, or factory method will fail and throw an
77 * {@code IllegalArgumentException} if the created method handle's type
78 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
79 *
80 * @author John Rose, JSR 292 EG
81 * @since 1.7
82 */
83 public class MethodHandles {
84
85 private MethodHandles() { } // do not instantiate
86
87 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
88
89 // See IMPL_LOOKUP below.
90
91 //// Method handle creation from ordinary methods.
92
93 /**
94 * Returns a {@link Lookup lookup object} with
95 * full capabilities to emulate all supported bytecode behaviors of the caller.
96 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
97 * Factory methods on the lookup object can create
98 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
99 * for any member that the caller has access to via bytecodes,
100 * including protected and private fields and methods.
101 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
102 * Do not store it in place where untrusted code can access it.
103 * <p>
104 * This method is caller sensitive, which means that it may return different
105 * values to different callers.
106 * @return a lookup object for the caller of this method, with private access
107 */
108 @CallerSensitive
109 @ForceInline // to ensure Reflection.getCallerClass optimization
110 public static Lookup lookup() {
111 return new Lookup(Reflection.getCallerClass());
112 }
113
114 /**
115 * This reflected$lookup method is the alternate implementation of
116 * the lookup method when being invoked by reflection.
117 */
118 @CallerSensitive
119 private static Lookup reflected$lookup() {
120 Class<?> caller = Reflection.getCallerClass();
121 if (caller.getClassLoader() == null) {
122 throw newIllegalArgumentException("illegal lookupClass: "+caller);
123 }
124 return new Lookup(caller);
125 }
126
127 /**
128 * Returns a {@link Lookup lookup object} which is trusted minimally.
129 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
130 * It can only be used to create method handles to public members of
131 * public classes in packages that are exported unconditionally.
132 * <p>
133 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
134 * of this lookup object will be {@link java.lang.Object}.
135 *
136 * @apiNote The use of Object is conventional, and because the lookup modes are
137 * limited, there is no special access provided to the internals of Object, its package
138 * or its module. Consequently, the lookup context of this lookup object will be the
139 * bootstrap class loader, which means it cannot find user classes.
140 *
141 * <p style="font-size:smaller;">
142 * <em>Discussion:</em>
143 * The lookup class can be changed to any other class {@code C} using an expression of the form
144 * {@link Lookup#in publicLookup().in(C.class)}.
145 * but may change the lookup context by virtue of changing the class loader.
146 * A public lookup object is always subject to
147 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
148 * Also, it cannot access
149 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
150 * @return a lookup object which is trusted minimally
151 *
152 * @revised 9
153 * @spec JPMS
154 */
155 public static Lookup publicLookup() {
156 return Lookup.PUBLIC_LOOKUP;
157 }
158
159 /**
160 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
161 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
162 * private access</a>, on a target class.
163 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
164 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
165 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
166 * the target class, then this check ensures that
167 * <ul>
168 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
169 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
170 * the target class to at least {@code m1}.</li>
171 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
172 * </ul>
173 * <p>
174 * If there is a security manager, its {@code checkPermission} method is called to
175 * check {@code ReflectPermission("suppressAccessChecks")}.
176 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
177 * was created by code in the caller module (or derived from a lookup object originally
178 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
179 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
180 * access to the caller.
181 * @param targetClass the target class
182 * @param lookup the caller lookup object
183 * @return a lookup object for the target class, with private access
184 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class
185 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
186 * @throws IllegalAccessException if the access check specified above fails
187 * @throws SecurityException if denied by the security manager
188 * @since 9
189 * @spec JPMS
190 * @see Lookup#dropLookupMode
191 */
192 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
193 if (lookup.allowedModes == Lookup.TRUSTED) {
194 return new Lookup(targetClass);
195 }
196
197 SecurityManager sm = System.getSecurityManager();
198 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
199 if (targetClass.isPrimitive())
200 throw new IllegalArgumentException(targetClass + " is a primitive class");
201 if (targetClass.isArray())
202 throw new IllegalArgumentException(targetClass + " is an array class");
203 Module targetModule = targetClass.getModule();
204 Module callerModule = lookup.lookupClass().getModule();
205 if (!callerModule.canRead(targetModule))
206 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
207 if (targetModule.isNamed()) {
208 String pn = targetClass.getPackageName();
209 assert pn.length() > 0 : "unnamed package cannot be in named module";
210 if (!targetModule.isOpen(pn, callerModule))
211 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
212 }
213 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
214 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
215 if (!callerModule.isNamed() && targetModule.isNamed()) {
216 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
217 if (logger != null) {
218 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
219 }
220 }
221 return new Lookup(targetClass);
222 }
223
224 /**
225 * Performs an unchecked "crack" of a
226 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
227 * The result is as if the user had obtained a lookup object capable enough
228 * to crack the target method handle, called
229 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
230 * on the target to obtain its symbolic reference, and then called
231 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
232 * to resolve the symbolic reference to a member.
233 * <p>
234 * If there is a security manager, its {@code checkPermission} method
235 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
236 * @param <T> the desired type of the result, either {@link Member} or a subtype
237 * @param target a direct method handle to crack into symbolic reference components
238 * @param expected a class object representing the desired result type {@code T}
239 * @return a reference to the method, constructor, or field object
240 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
241 * @exception NullPointerException if either argument is {@code null}
242 * @exception IllegalArgumentException if the target is not a direct method handle
243 * @exception ClassCastException if the member is not of the expected type
244 * @since 1.8
245 */
246 public static <T extends Member> T
247 reflectAs(Class<T> expected, MethodHandle target) {
248 SecurityManager smgr = System.getSecurityManager();
249 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
250 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
251 return lookup.revealDirect(target).reflectAs(expected, lookup);
252 }
253 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
254 private static final java.security.Permission ACCESS_PERMISSION =
255 new ReflectPermission("suppressAccessChecks");
256
257 /**
258 * A <em>lookup object</em> is a factory for creating method handles,
259 * when the creation requires access checking.
260 * Method handles do not perform
261 * access checks when they are called, but rather when they are created.
262 * Therefore, method handle access
263 * restrictions must be enforced when a method handle is created.
264 * The caller class against which those restrictions are enforced
265 * is known as the {@linkplain #lookupClass() lookup class}.
266 * <p>
267 * A lookup class which needs to create method handles will call
268 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
269 * When the {@code Lookup} factory object is created, the identity of the lookup class is
270 * determined, and securely stored in the {@code Lookup} object.
271 * The lookup class (or its delegates) may then use factory methods
272 * on the {@code Lookup} object to create method handles for access-checked members.
273 * This includes all methods, constructors, and fields which are allowed to the lookup class,
274 * even private ones.
275 *
276 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
277 * The factory methods on a {@code Lookup} object correspond to all major
278 * use cases for methods, constructors, and fields.
279 * Each method handle created by a factory method is the functional
280 * equivalent of a particular <em>bytecode behavior</em>.
281 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
282 * Here is a summary of the correspondence between these factory methods and
283 * the behavior of the resulting method handles:
284 * <table class="striped">
285 * <caption style="display:none">lookup method behaviors</caption>
286 * <thead>
287 * <tr>
288 * <th scope="col"><a id="equiv"></a>lookup expression</th>
289 * <th scope="col">member</th>
290 * <th scope="col">bytecode behavior</th>
291 * </tr>
292 * </thead>
293 * <tbody>
294 * <tr>
295 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
296 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
297 * </tr>
298 * <tr>
299 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
300 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
301 * </tr>
302 * <tr>
303 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
304 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
305 * </tr>
306 * <tr>
307 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
308 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
309 * </tr>
310 * <tr>
311 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
312 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
313 * </tr>
314 * <tr>
315 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
316 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
317 * </tr>
318 * <tr>
319 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
320 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
321 * </tr>
322 * <tr>
323 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
324 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
325 * </tr>
326 * <tr>
327 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
328 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
329 * </tr>
330 * <tr>
331 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
332 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
333 * </tr>
334 * <tr>
335 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
336 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
337 * </tr>
338 * <tr>
339 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
340 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
341 * </tr>
342 * <tr>
343 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
344 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
345 * </tr>
346 * <tr>
347 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
348 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
349 * </tr>
350 * </tbody>
351 * </table>
352 *
353 * Here, the type {@code C} is the class or interface being searched for a member,
354 * documented as a parameter named {@code refc} in the lookup methods.
355 * The method type {@code MT} is composed from the return type {@code T}
356 * and the sequence of argument types {@code A*}.
357 * The constructor also has a sequence of argument types {@code A*} and
358 * is deemed to return the newly-created object of type {@code C}.
359 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
360 * The formal parameter {@code this} stands for the self-reference of type {@code C};
361 * if it is present, it is always the leading argument to the method handle invocation.
362 * (In the case of some {@code protected} members, {@code this} may be
363 * restricted in type to the lookup class; see below.)
364 * The name {@code arg} stands for all the other method handle arguments.
365 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
366 * stands for a null reference if the accessed method or field is static,
367 * and {@code this} otherwise.
368 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
369 * for reflective objects corresponding to the given members.
370 * <p>
371 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
372 * as if by {@code ldc CONSTANT_Class}.
373 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
374 * <p>
375 * In cases where the given member is of variable arity (i.e., a method or constructor)
376 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
377 * In all other cases, the returned method handle will be of fixed arity.
378 * <p style="font-size:smaller;">
379 * <em>Discussion:</em>
380 * The equivalence between looked-up method handles and underlying
381 * class members and bytecode behaviors
382 * can break down in a few ways:
383 * <ul style="font-size:smaller;">
384 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
385 * the lookup can still succeed, even when there is no equivalent
386 * Java expression or bytecoded constant.
387 * <li>Likewise, if {@code T} or {@code MT}
388 * is not symbolically accessible from the lookup class's loader,
389 * the lookup can still succeed.
390 * For example, lookups for {@code MethodHandle.invokeExact} and
391 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
392 * <li>If there is a security manager installed, it can forbid the lookup
393 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
394 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
395 * constant is not subject to security manager checks.
396 * <li>If the looked-up method has a
397 * <a href="MethodHandle.html#maxarity">very large arity</a>,
398 * the method handle creation may fail with an
399 * {@code IllegalArgumentException}, due to the method handle type having
400 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
401 * </ul>
402 *
403 * <h1><a id="access"></a>Access checking</h1>
404 * Access checks are applied in the factory methods of {@code Lookup},
405 * when a method handle is created.
406 * This is a key difference from the Core Reflection API, since
407 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
408 * performs access checking against every caller, on every call.
409 * <p>
410 * All access checks start from a {@code Lookup} object, which
411 * compares its recorded lookup class against all requests to
412 * create method handles.
413 * A single {@code Lookup} object can be used to create any number
414 * of access-checked method handles, all checked against a single
415 * lookup class.
416 * <p>
417 * A {@code Lookup} object can be shared with other trusted code,
418 * such as a metaobject protocol.
419 * A shared {@code Lookup} object delegates the capability
420 * to create method handles on private members of the lookup class.
421 * Even if privileged code uses the {@code Lookup} object,
422 * the access checking is confined to the privileges of the
423 * original lookup class.
424 * <p>
425 * A lookup can fail, because
426 * the containing class is not accessible to the lookup class, or
427 * because the desired class member is missing, or because the
428 * desired class member is not accessible to the lookup class, or
429 * because the lookup object is not trusted enough to access the member.
430 * In any of these cases, a {@code ReflectiveOperationException} will be
431 * thrown from the attempted lookup. The exact class will be one of
432 * the following:
433 * <ul>
434 * <li>NoSuchMethodException — if a method is requested but does not exist
435 * <li>NoSuchFieldException — if a field is requested but does not exist
436 * <li>IllegalAccessException — if the member exists but an access check fails
437 * </ul>
438 * <p>
439 * In general, the conditions under which a method handle may be
440 * looked up for a method {@code M} are no more restrictive than the conditions
441 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
442 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
443 * a method handle lookup will generally raise a corresponding
444 * checked exception, such as {@code NoSuchMethodException}.
445 * And the effect of invoking the method handle resulting from the lookup
446 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
447 * to executing the compiled, verified, and resolved call to {@code M}.
448 * The same point is true of fields and constructors.
449 * <p style="font-size:smaller;">
450 * <em>Discussion:</em>
451 * Access checks only apply to named and reflected methods,
452 * constructors, and fields.
453 * Other method handle creation methods, such as
454 * {@link MethodHandle#asType MethodHandle.asType},
455 * do not require any access checks, and are used
456 * independently of any {@code Lookup} object.
457 * <p>
458 * If the desired member is {@code protected}, the usual JVM rules apply,
459 * including the requirement that the lookup class must either be in the
460 * same package as the desired member, or must inherit that member.
461 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
462 * In addition, if the desired member is a non-static field or method
463 * in a different package, the resulting method handle may only be applied
464 * to objects of the lookup class or one of its subclasses.
465 * This requirement is enforced by narrowing the type of the leading
466 * {@code this} parameter from {@code C}
467 * (which will necessarily be a superclass of the lookup class)
468 * to the lookup class itself.
469 * <p>
470 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
471 * that the receiver argument must match both the resolved method <em>and</em>
472 * the current class. Again, this requirement is enforced by narrowing the
473 * type of the leading parameter to the resulting method handle.
474 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
475 * <p>
476 * The JVM represents constructors and static initializer blocks as internal methods
477 * with special names ({@code "<init>"} and {@code "<clinit>"}).
478 * The internal syntax of invocation instructions allows them to refer to such internal
479 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
480 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
481 * <p>
482 * If the relationship between nested types is expressed directly through the
483 * {@code NestHost} and {@code NestMembers} attributes
484 * (see the Java Virtual Machine Specification, sections 4.7.28 and 4.7.29),
485 * then the associated {@code Lookup} object provides direct access to
486 * the lookup class and all of its nestmates
487 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
488 * Otherwise, access between nested classes is obtained by the Java compiler creating
489 * a wrapper method to access a private method of another class in the same nest.
490 * For example, a nested class {@code C.D}
491 * can access private members within other related classes such as
492 * {@code C}, {@code C.D.E}, or {@code C.B},
493 * but the Java compiler may need to generate wrapper methods in
494 * those related classes. In such cases, a {@code Lookup} object on
495 * {@code C.E} would be unable to access those private members.
496 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
497 * which can transform a lookup on {@code C.E} into one on any of those other
498 * classes, without special elevation of privilege.
499 * <p>
500 * The accesses permitted to a given lookup object may be limited,
501 * according to its set of {@link #lookupModes lookupModes},
502 * to a subset of members normally accessible to the lookup class.
503 * For example, the {@link MethodHandles#publicLookup publicLookup}
504 * method produces a lookup object which is only allowed to access
505 * public members in public classes of exported packages.
506 * The caller sensitive method {@link MethodHandles#lookup lookup}
507 * produces a lookup object with full capabilities relative to
508 * its caller class, to emulate all supported bytecode behaviors.
509 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
510 * with fewer access modes than the original lookup object.
511 *
512 * <p style="font-size:smaller;">
513 * <a id="privacc"></a>
514 * <em>Discussion of private access:</em>
515 * We say that a lookup has <em>private access</em>
516 * if its {@linkplain #lookupModes lookup modes}
517 * include the possibility of accessing {@code private} members
518 * (which includes the private members of nestmates).
519 * As documented in the relevant methods elsewhere,
520 * only lookups with private access possess the following capabilities:
521 * <ul style="font-size:smaller;">
522 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
523 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
524 * such as {@code Class.forName}
525 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
526 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
527 * for classes accessible to the lookup class
528 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
529 * within the same package member
530 * </ul>
531 * <p style="font-size:smaller;">
532 * Each of these permissions is a consequence of the fact that a lookup object
533 * with private access can be securely traced back to an originating class,
534 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
535 * can be reliably determined and emulated by method handles.
536 *
537 * <h1><a id="secmgr"></a>Security manager interactions</h1>
538 * Although bytecode instructions can only refer to classes in
539 * a related class loader, this API can search for methods in any
540 * class, as long as a reference to its {@code Class} object is
541 * available. Such cross-loader references are also possible with the
542 * Core Reflection API, and are impossible to bytecode instructions
543 * such as {@code invokestatic} or {@code getfield}.
544 * There is a {@linkplain java.lang.SecurityManager security manager API}
545 * to allow applications to check such cross-loader references.
546 * These checks apply to both the {@code MethodHandles.Lookup} API
547 * and the Core Reflection API
548 * (as found on {@link java.lang.Class Class}).
549 * <p>
550 * If a security manager is present, member and class lookups are subject to
551 * additional checks.
552 * From one to three calls are made to the security manager.
553 * Any of these calls can refuse access by throwing a
554 * {@link java.lang.SecurityException SecurityException}.
555 * Define {@code smgr} as the security manager,
556 * {@code lookc} as the lookup class of the current lookup object,
557 * {@code refc} as the containing class in which the member
558 * is being sought, and {@code defc} as the class in which the
559 * member is actually defined.
560 * (If a class or other type is being accessed,
561 * the {@code refc} and {@code defc} values are the class itself.)
562 * The value {@code lookc} is defined as <em>not present</em>
563 * if the current lookup object does not have
564 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
565 * The calls are made according to the following rules:
566 * <ul>
567 * <li><b>Step 1:</b>
568 * If {@code lookc} is not present, or if its class loader is not
569 * the same as or an ancestor of the class loader of {@code refc},
570 * then {@link SecurityManager#checkPackageAccess
571 * smgr.checkPackageAccess(refcPkg)} is called,
572 * where {@code refcPkg} is the package of {@code refc}.
573 * <li><b>Step 2a:</b>
574 * If the retrieved member is not public and
575 * {@code lookc} is not present, then
576 * {@link SecurityManager#checkPermission smgr.checkPermission}
577 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
578 * <li><b>Step 2b:</b>
579 * If the retrieved class has a {@code null} class loader,
580 * and {@code lookc} is not present, then
581 * {@link SecurityManager#checkPermission smgr.checkPermission}
582 * with {@code RuntimePermission("getClassLoader")} is called.
583 * <li><b>Step 3:</b>
584 * If the retrieved member is not public,
585 * and if {@code lookc} is not present,
586 * and if {@code defc} and {@code refc} are different,
587 * then {@link SecurityManager#checkPackageAccess
588 * smgr.checkPackageAccess(defcPkg)} is called,
589 * where {@code defcPkg} is the package of {@code defc}.
590 * </ul>
591 * Security checks are performed after other access checks have passed.
592 * Therefore, the above rules presuppose a member or class that is public,
593 * or else that is being accessed from a lookup class that has
594 * rights to access the member or class.
595 *
596 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
597 * A small number of Java methods have a special property called caller sensitivity.
598 * A <em>caller-sensitive</em> method can behave differently depending on the
599 * identity of its immediate caller.
600 * <p>
601 * If a method handle for a caller-sensitive method is requested,
602 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
603 * but they take account of the lookup class in a special way.
604 * The resulting method handle behaves as if it were called
605 * from an instruction contained in the lookup class,
606 * so that the caller-sensitive method detects the lookup class.
607 * (By contrast, the invoker of the method handle is disregarded.)
608 * Thus, in the case of caller-sensitive methods,
609 * different lookup classes may give rise to
610 * differently behaving method handles.
611 * <p>
612 * In cases where the lookup object is
613 * {@link MethodHandles#publicLookup() publicLookup()},
614 * or some other lookup object without
615 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
616 * the lookup class is disregarded.
617 * In such cases, no caller-sensitive method handle can be created,
618 * access is forbidden, and the lookup fails with an
619 * {@code IllegalAccessException}.
620 * <p style="font-size:smaller;">
621 * <em>Discussion:</em>
622 * For example, the caller-sensitive method
623 * {@link java.lang.Class#forName(String) Class.forName(x)}
624 * can return varying classes or throw varying exceptions,
625 * depending on the class loader of the class that calls it.
626 * A public lookup of {@code Class.forName} will fail, because
627 * there is no reasonable way to determine its bytecode behavior.
628 * <p style="font-size:smaller;">
629 * If an application caches method handles for broad sharing,
630 * it should use {@code publicLookup()} to create them.
631 * If there is a lookup of {@code Class.forName}, it will fail,
632 * and the application must take appropriate action in that case.
633 * It may be that a later lookup, perhaps during the invocation of a
634 * bootstrap method, can incorporate the specific identity
635 * of the caller, making the method accessible.
636 * <p style="font-size:smaller;">
637 * The function {@code MethodHandles.lookup} is caller sensitive
638 * so that there can be a secure foundation for lookups.
639 * Nearly all other methods in the JSR 292 API rely on lookup
640 * objects to check access requests.
641 *
642 * @revised 9
643 */
644 public static final
645 class Lookup {
646 /** The class on behalf of whom the lookup is being performed. */
647 private final Class<?> lookupClass;
648
649 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
650 private final int allowedModes;
651
652 static {
653 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
654 }
655
656 /** A single-bit mask representing {@code public} access,
657 * which may contribute to the result of {@link #lookupModes lookupModes}.
658 * The value, {@code 0x01}, happens to be the same as the value of the
659 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
660 */
661 public static final int PUBLIC = Modifier.PUBLIC;
662
663 /** A single-bit mask representing {@code private} access,
664 * which may contribute to the result of {@link #lookupModes lookupModes}.
665 * The value, {@code 0x02}, happens to be the same as the value of the
666 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
667 */
668 public static final int PRIVATE = Modifier.PRIVATE;
669
670 /** A single-bit mask representing {@code protected} access,
671 * which may contribute to the result of {@link #lookupModes lookupModes}.
672 * The value, {@code 0x04}, happens to be the same as the value of the
673 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
674 */
675 public static final int PROTECTED = Modifier.PROTECTED;
676
677 /** A single-bit mask representing {@code package} access (default access),
678 * which may contribute to the result of {@link #lookupModes lookupModes}.
679 * The value is {@code 0x08}, which does not correspond meaningfully to
680 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
681 */
682 public static final int PACKAGE = Modifier.STATIC;
683
684 /** A single-bit mask representing {@code module} access (default access),
685 * which may contribute to the result of {@link #lookupModes lookupModes}.
686 * The value is {@code 0x10}, which does not correspond meaningfully to
687 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
688 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
689 * with this lookup mode can access all public types in the module of the
690 * lookup class and public types in packages exported by other modules
691 * to the module of the lookup class.
692 * @since 9
693 * @spec JPMS
694 */
695 public static final int MODULE = PACKAGE << 1;
696
697 /** A single-bit mask representing {@code unconditional} access
698 * which may contribute to the result of {@link #lookupModes lookupModes}.
699 * The value is {@code 0x20}, which does not correspond meaningfully to
700 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
701 * A {@code Lookup} with this lookup mode assumes {@linkplain
702 * java.lang.Module#canRead(java.lang.Module) readability}.
703 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
704 * with this lookup mode can access all public members of public types
705 * of all modules where the type is in a package that is {@link
706 * java.lang.Module#isExported(String) exported unconditionally}.
707 * @since 9
708 * @spec JPMS
709 * @see #publicLookup()
710 */
711 public static final int UNCONDITIONAL = PACKAGE << 2;
712
713 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
714 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
715 private static final int TRUSTED = -1;
716
717 private static int fixmods(int mods) {
718 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
719 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
720 }
721
722 /** Tells which class is performing the lookup. It is this class against
723 * which checks are performed for visibility and access permissions.
724 * <p>
725 * The class implies a maximum level of access permission,
726 * but the permissions may be additionally limited by the bitmask
727 * {@link #lookupModes lookupModes}, which controls whether non-public members
728 * can be accessed.
729 * @return the lookup class, on behalf of which this lookup object finds members
730 */
731 public Class<?> lookupClass() {
732 return lookupClass;
733 }
734
735 // This is just for calling out to MethodHandleImpl.
736 private Class<?> lookupClassOrNull() {
737 return (allowedModes == TRUSTED) ? null : lookupClass;
738 }
739
740 /** Tells which access-protection classes of members this lookup object can produce.
741 * The result is a bit-mask of the bits
742 * {@linkplain #PUBLIC PUBLIC (0x01)},
743 * {@linkplain #PRIVATE PRIVATE (0x02)},
744 * {@linkplain #PROTECTED PROTECTED (0x04)},
745 * {@linkplain #PACKAGE PACKAGE (0x08)},
746 * {@linkplain #MODULE MODULE (0x10)},
747 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
748 * <p>
749 * A freshly-created lookup object
750 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
751 * all possible bits set, except {@code UNCONDITIONAL}.
752 * A lookup object on a new lookup class
753 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
754 * may have some mode bits set to zero.
755 * Mode bits can also be
756 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
757 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
758 * The purpose of this is to restrict access via the new lookup object,
759 * so that it can access only names which can be reached by the original
760 * lookup object, and also by the new lookup class.
761 * @return the lookup modes, which limit the kinds of access performed by this lookup object
762 * @see #in
763 * @see #dropLookupMode
764 *
765 * @revised 9
766 * @spec JPMS
767 */
768 public int lookupModes() {
769 return allowedModes & ALL_MODES;
770 }
771
772 /** Embody the current class (the lookupClass) as a lookup class
773 * for method handle creation.
774 * Must be called by from a method in this package,
775 * which in turn is called by a method not in this package.
776 */
777 Lookup(Class<?> lookupClass) {
778 this(lookupClass, FULL_POWER_MODES);
779 }
780
781 private Lookup(Class<?> lookupClass, int allowedModes) {
782 this.lookupClass = lookupClass;
783 this.allowedModes = allowedModes;
784 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
785 }
786
787 /**
788 * Creates a lookup on the specified new lookup class.
789 * The resulting object will report the specified
790 * class as its own {@link #lookupClass() lookupClass}.
791 * <p>
792 * However, the resulting {@code Lookup} object is guaranteed
793 * to have no more access capabilities than the original.
794 * In particular, access capabilities can be lost as follows:<ul>
795 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
796 * the new lookup class is in a different module {@code M}, then no members, not
797 * even public members in {@code M}'s exported packages, will be accessible.
798 * The exception to this is when this lookup is {@link #publicLookup()
799 * publicLookup}, in which case {@code PUBLIC} access is not lost.
800 * <li>If the old lookup class is in an unnamed module, and the new lookup class
801 * is a different module then {@link #MODULE MODULE} access is lost.
802 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
803 * <li>If the new lookup class is in a different package
804 * than the old one, protected and default (package) members will not be accessible.
805 * <li>If the new lookup class is not within the same package member
806 * as the old one, private members will not be accessible, and protected members
807 * will not be accessible by virtue of inheritance.
808 * (Protected members may continue to be accessible because of package sharing.)
809 * <li>If the new lookup class is not accessible to the old lookup class,
810 * then no members, not even public members, will be accessible.
811 * (In all other cases, public members will continue to be accessible.)
812 * </ul>
813 * <p>
814 * The resulting lookup's capabilities for loading classes
815 * (used during {@link #findClass} invocations)
816 * are determined by the lookup class' loader,
817 * which may change due to this operation.
818 *
819 * @param requestedLookupClass the desired lookup class for the new lookup object
820 * @return a lookup object which reports the desired lookup class, or the same object
821 * if there is no change
822 * @throws IllegalArgumentException if {@code requestedLookupClass} is
823 * a primitive type or array class
824 * @throws NullPointerException if the argument is null
825 *
826 * @revised 9
827 * @spec JPMS
828 */
829 public Lookup in(Class<?> requestedLookupClass) {
830 Objects.requireNonNull(requestedLookupClass);
831 if (requestedLookupClass.isPrimitive())
832 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
833 if (requestedLookupClass.isArray())
834 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
835
836 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
837 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
838 if (requestedLookupClass == this.lookupClass)
839 return this; // keep same capabilities
840 int newModes = (allowedModes & FULL_POWER_MODES);
841 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
842 // Need to drop all access when teleporting from a named module to another
843 // module. The exception is publicLookup where PUBLIC is not lost.
844 if (this.lookupClass.getModule().isNamed()
845 && (this.allowedModes & UNCONDITIONAL) == 0)
846 newModes = 0;
847 else
848 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
849 }
850 if ((newModes & PACKAGE) != 0
851 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
852 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
853 }
854 // Allow nestmate lookups to be created without special privilege:
855 if ((newModes & PRIVATE) != 0
856 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
857 newModes &= ~(PRIVATE|PROTECTED);
858 }
859 if ((newModes & PUBLIC) != 0
860 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
861 // The requested class it not accessible from the lookup class.
862 // No permissions.
863 newModes = 0;
864 }
865
866 checkUnprivilegedlookupClass(requestedLookupClass);
867 return new Lookup(requestedLookupClass, newModes);
868 }
869
870
871 /**
872 * Creates a lookup on the same lookup class which this lookup object
873 * finds members, but with a lookup mode that has lost the given lookup mode.
874 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
875 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
876 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
877 * dropped and so the resulting lookup mode will never have these access capabilities.
878 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
879 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
880 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
881 * is dropped then the resulting lookup has no access.
882 * @param modeToDrop the lookup mode to drop
883 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
884 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
885 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
886 * @see MethodHandles#privateLookupIn
887 * @since 9
888 */
889 public Lookup dropLookupMode(int modeToDrop) {
890 int oldModes = lookupModes();
891 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
892 switch (modeToDrop) {
893 case PUBLIC: newModes &= ~(ALL_MODES); break;
894 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
895 case PACKAGE: newModes &= ~(PRIVATE); break;
896 case PROTECTED:
897 case PRIVATE:
898 case UNCONDITIONAL: break;
899 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
900 }
901 if (newModes == oldModes) return this; // return self if no change
902 return new Lookup(lookupClass(), newModes);
903 }
904
905 /**
906 * Defines a class to the same class loader and in the same runtime package and
907 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
908 * {@linkplain #lookupClass() lookup class}.
909 *
910 * This method is equivalent to calling
911 * {@link #defineClass(byte[], ClassProperty[])
912 * defineClass(bytes, (ClassProperty[])null)}.
913 *
914 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
915 * {@link #PACKAGE PACKAGE} access as default (package) members will be
916 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
917 * that the lookup object was created by a caller in the runtime package (or derived
918 * from a lookup originally created by suitably privileged code to a target class in
919 * the runtime package). </p>
920 *
921 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
922 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
923 * same package as the lookup class. </p>
924 *
925 * <p> This method does not run the class initializer. The class initializer may
926 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
927 * Specification</em>. </p>
928 *
929 * <p> If there is a security manager, its {@code checkPermission} method is first called
930 * to check {@code RuntimePermission("defineClass")}. </p>
931 *
932 * @param bytes the class bytes
933 * @return the {@code Class} object for the class
934 * @throws IllegalArgumentException the bytes are for a class in a different package
935 * to the lookup class
936 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
937 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
938 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
939 * @throws SecurityException if denied by the security manager
940 * @throws NullPointerException if {@code bytes} is {@code null}
941 * @since 9
942 * @spec JPMS
943 * @see Lookup#privateLookupIn
944 * @see Lookup#dropLookupMode
945 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
946 */
947 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
948 return defineClass(bytes, (ClassProperty[])null);
949 }
950
951 /**
952 * Defines a class to the same class loader and in the same runtime package
953 * and {@linkplain java.security.ProtectionDomain protection domain} as
954 * this lookup's {@linkplain #lookupClass() lookup class}.
955 * The {@code props} parameter specifies the properties of the class.
956 *
957 * <p> A class can be defined with the following properties:
958 * <ul>
959 * <li>A {@linkplain ClassProperty#NESTMATE <em>nestmate</em>} of the lookup class,
960 * i.e. in the same {@linkplain Class#getNestHost nest}
961 * of the lookup class. The class will have access to the private members
962 * of all classes and interfaces in the same nest.
963 * </li>
964 * <li>A {@linkplain ClassProperty#HIDDEN <em>hidden</em>} class,
965 * i.e. a class cannot be referenced by other classes.
966 * A hidden class has the following properties:
967 * <ul>
968 * <li>Naming:
969 * The name of this class is derived from the name of
970 * the class in the class bytes so that the class name does not
971 * collide with other classes defined to the same class loader.
972 * <li>Class resolution:
973 * The Java virtual machine does not find a hidden class with
974 * its name. A hidden class can reference its members
975 * locally with the name of the class in the class bytes as if
976 * a non-hidden class. The name returned by {@link Class#getName()}
977 * is not known when the class bytes are generated.
978 * <li>Class retransformation:
979 * The class is not modifiable by Java agents or tool agents using
980 * the <a href="{@docRoot}/../specs/jvmti.html">JVM Tool Interface</a>.
981 * </ul>
982 * </li>
983 * <li>A {@linkplain ClassProperty#WEAK <em>weak</em>} class,
984 * i.e. a class may be unloaded even if its defining class loader is
985 * <a href="../ref/package.html#reachability">reachable</a>,
986 * as if the defining class loader would only hold a
987 * {@linkplain java.lang.ref.WeakReference weak reference} of
988 * the class.
989 * A weak class is hidden. If the {@code WEAK} property is set,
990 * then it implies that {@code HIDDEN} property is also set.</li>
991 * </ul>
992 *
993 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must
994 * include {@link #PACKAGE PACKAGE} access as default (package) members
995 * will be accessible to the class. The {@code PACKAGE} lookup mode serves
996 * to authenticate that the lookup object was created by a caller in
997 * the runtime package (or derived from a lookup originally created by
998 * suitably privileged code to a target class in the runtime package).
999 * If the class is defined as a {@linkplain ClassProperty#NESTMATE nestmate}
1000 * then the {@linkplain #lookupModes() lookup modes} for this lookup must
1001 * include {@link #PRIVATE PRIVATE} access. </p>
1002 *
1003 * <p> The {@code bytes} parameter is the class bytes of a valid class file
1004 * (as defined by the <em>The Java Virtual Machine Specification</em>)
1005 * with a class name in the same package as the lookup class.
1006 * The class bytes of a nestmate class must not contain
1007 * the {@code NestHost} attribute nor the {@code NestMembers} attribute. </p>
1008 *
1009 * <p> If there is a security manager, its {@code checkPermission} method is first called
1010 * to check {@code RuntimePermission("defineClass")}. </p>
1011 *
1012 * <p> This method does not run the class initializer. The class initializer
1013 * may run at a later time, as detailed in section 12.4 of the The Java Language Specification.
1014 *
1015 * <p> The class can obtain {@code classData} by calling
1016 * the {@link Lookup#classData()} method of its {@code Lookup} object.
1017 *
1018 * @apiNote An implementation of the Java Progamming Language may
1019 * unload classes as specified in section 12.7 of the Java Language Specification.
1020 * A class or interface may be unloaded if and only if
1021 * its defining class loader may be reclaimed by the garbage collector.
1022 * If the implementation supports class loading, a weak class
1023 * may become weakly reachable as if the defining class loader would
1024 * only hold a {@linkplain java.lang.ref.WeakReference weak reference}
1025 * of the class.
1026 *
1027 * @param bytes the class bytes
1028 * @param props {@linkplain ClassProperty class properties}
1029 * @return the {@code Class} object for the class
1030 *
1031 * @throws IllegalArgumentException the bytes are for a class in a different package
1032 * to the lookup class
1033 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access, or
1034 * if {@code properties} contains {@code NESTMATE} but this lookup
1035 * does not have {@code PRIVATE} access
1036 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1037 * verified ({@code VerifyError}), is already defined,
1038 * or another linkage error occurs
1039 * @throws SecurityException if denied by the security manager
1040 * @throws NullPointerException if {@code bytes} is {@code null}
1041 *
1042 * @since 12
1043 * @jls 12.7 Unloading of Classes and Interfaces
1044 * @see Lookup#privateLookupIn(Class, Lookup)
1045 * @see Lookup#dropLookupMode(int)
1046 */
1047 public Class<?> defineClass(byte[] bytes, ClassProperty... props) throws IllegalAccessException {
1048 Objects.requireNonNull(bytes);
1049
1050 // clone the properties before access
1051 Set<ClassProperty> properties;
1052 if (props == null || props.length == 0) {
1053 properties = EMPTY_PROPS;
1054 } else {
1055 properties = Set.of(props);
1056 }
1057
1058 // Is it ever possible to create Lookup for int.class or Object[].class?
1059 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
1060
1061 if ((lookupModes() & PACKAGE) == 0){
1062 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1063 }
1064
1065 if (properties.contains(NESTMATE) && (lookupModes() & PRIVATE) == 0){
1066 throw new IllegalAccessException("Lookup does not have PRIVATE access");
1067 }
1068
1069 assert (lookupModes() & (MODULE | PUBLIC)) != 0;
1070
1071 SecurityManager sm = System.getSecurityManager();
1072 if (sm != null)
1073 sm.checkPermission(new RuntimePermission("defineClass"));
1074
1075 return defineClassWithNoCheck(bytes, classPropertiesToFlags(properties));
1076 }
1077
1078 /**
1079 * Defines a class to the same class loader and in the same runtime package
1080 * and {@linkplain java.security.ProtectionDomain protection domain} as
1081 * this lookup's {@linkplain #lookupClass() lookup class} with
1082 * the given class properties and {@code classData}.
1083 *
1084 * <p> This method defines a class as if calling
1085 * {@link #defineClass(byte[], ClassProperty...) defineClass(bytes, props)}
1086 * and then the class initializer with an injected the {@code classData}
1087 * as a pre-initialized static unnamed field.
1088 * The injected pre-initialized static unnamed field can be
1089 * obtained by calling the {@link Lookup#classData()} method of
1090 * its {@code Lookup} object.
1091 *
1092 * <p> If there is a security manager, its {@code checkPermission} method is first called
1093 * to check {@code RuntimePermission("defineClass")}. </p>
1094 *
1095 * @apiNote
1096 * This method initializes the class, as opposed to the {@link #defineClass(byte[], ClassProperty...)}
1097 * method which does not invoke {@code <clinit>}, because the returned {@code Class}
1098 * is as if it contains a private static unnamed field that is initialized to
1099 * the given {@code classData} along with other declared static fields
1100 * via {@code <clinit>}.
1101 *
1102 * @param bytes the class bytes
1103 * @param classData pre-initialized class data
1104 * @param props {@linkplain ClassProperty class properties}
1105 * @return the {@code Class} object for the class
1106 *
1107 * @throws IllegalArgumentException the bytes are for a class in a different package
1108 * to the lookup class
1109 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access, or
1110 * if {@code properties} contains {@code NESTMATE} but this lookup
1111 * does not have {@code PRIVATE} access
1112 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
1113 * verified ({@code VerifyError}), is already defined,
1114 * or another linkage error occurs
1115 * @throws SecurityException if denied by the security manager
1116 * @throws NullPointerException if {@code bytes} or {@code classData} is {@code null}
1117 *
1118 * @since 12
1119 * @jls 12.7 Unloading of Classes and Interfaces
1120 * @see Lookup#privateLookupIn(Class, Lookup)
1121 * @see Lookup#dropLookupMode(int)
1122 */
1123 public Class<?> defineClassWithClassData(byte[] bytes, Object classData, ClassProperty... props)
1124 throws IllegalAccessException
1125 {
1126 Objects.requireNonNull(bytes);
1127 Objects.requireNonNull(classData);
1128
1129 // Is it ever possible to create Lookup for int.class or Object[].class?
1130 assert !lookupClass.isPrimitive() && !lookupClass.isArray();
1131
1132 if ((lookupModes() & PACKAGE) == 0){
1133 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1134 }
1135
1136 Set<ClassProperty> properties;
1137 if (props == null || props.length == 0) {
1138 properties = EMPTY_PROPS;
1139 } else {
1140 properties = Set.of(props);
1141 }
1142
1143 if (properties.contains(NESTMATE) && (lookupModes() & PRIVATE) == 0){
1144 throw new IllegalAccessException("Lookup does not have PRIVATE access");
1145 }
1146
1147 assert (lookupModes() & (MODULE | PUBLIC)) != 0;
1148
1149 SecurityManager sm = System.getSecurityManager();
1150 if (sm != null)
1151 sm.checkPermission(new RuntimePermission("defineClass"));
1152
1153 return defineClassWithNoCheck(bytes, classPropertiesToFlags(properties), classData);
1154 }
1155
1156 private static int classPropertiesToFlags(Set<ClassProperty> props) {
1157 if (props.isEmpty()) return 0;
1158
1159 int flags = 0;
1160 for (ClassProperty cp : props) {
1161 flags |= cp.flag;
1162 if (cp == WEAK) {
1163 // weak class property implies hidden
1164 flags |= HIDDEN.flag;
1165 }
1166 }
1167 return flags;
1168 }
1169
1170 /**
1171 * Returns the class data associated with this lookup class.
1172 * If this lookup class was defined via
1173 * {@link #defineClassWithClassData(byte[], Object, ClassProperty...)
1174 * defineClassWithClassData(bytes, classData, properties)}
1175 * then the supplied {@code classData} object is returned; otherwise,
1176 * {@code null}.
1177 *
1178 * <p> This method will invoke the static class initializer of
1179 * this lookup class if it has not been initialized.
1180 *
1181 * @apiNote
1182 * A class data can be considered as
1183 * private static unnamed field that has been pre-initialized
1184 * and supplied at define class time.
1185 *
1186 * <p> For example a class can pack one or more pre-initialized objects
1187 * in a {@code List} as the class data and at class initialization
1188 * time unpack them for subsequent access.
1189 * The class data is {@code List.of(o1, o2, o3....)}
1190 * passed to {@link #defineClassWithClassData(byte[], Object, ClassProperty...)} where
1191 * {@code <clinit>} of the class bytes does the following:
1192 *
1193 * <pre>{@code
1194 * private static final T t;
1195 * private static final R r;
1196 * static {
1197 * List<Object> data = (List<Object>) MethodHandles.lookup().classData();
1198 * t = (T)data.get(0);
1199 * r = (R)data.get(1);
1200 * }
1201 *}</pre>
1202 *
1203 * @return the class data if this lookup class was defined via
1204 * {@link #defineClassWithClassData(byte[], Object, ClassProperty...)}; otherwise {@code null}.
1205 *
1206 * @throws IllegalAccessException if this lookup does not have {@code PRIVATE} access
1207 * @since 12
1208 */
1209 public Object classData() throws IllegalAccessException {
1210 if ((lookupModes() & PRIVATE) == 0){
1211 throw new IllegalAccessException("Lookup does not have PRIVATE access");
1212 }
1213
1214 // should we allow clearing? getAndClearClassData
1215 return CLASS_DATA_MAP.get(lookupClass);
1216 }
1217
1218 // package-private
1219 static final int HIDDEN_NESTMATE = NESTMATE_CLASS|NONFINDABLE_CLASS|ACCESS_VM_ANNOTATIONS;
1220 static final int WEAK_HIDDEN_NESTMATE = WEAK_CLASS|NESTMATE_CLASS|NONFINDABLE_CLASS|ACCESS_VM_ANNOTATIONS;
1221 static final Set<ClassProperty> EMPTY_PROPS = Set.of();
1222
1223 Class<?> defineClassWithNoCheck(byte[] bytes, int flags) {
1224 return defineClassWithNoCheck(bytes, flags, null);
1225 }
1226
1227 Class<?> defineClassWithNoCheck(byte[] bytes, int flags, Object classData) {
1228 // Can't use lambda during bootstrapping
1229 // parse class bytes to get class name (in internal form)
1230 bytes = bytes.clone();
1231 String name;
1232 try {
1233 ClassReader reader = new ClassReader(bytes);
1234 name = reader.getClassName();
1235 } catch (RuntimeException e) {
1236 // ASM exceptions are poorly specified
1237 ClassFormatError cfe = new ClassFormatError();
1238 cfe.initCause(e);
1239 throw cfe;
1240 }
1241
1242 // get package and class name in binary form
1243 String cn, pn;
1244 int index = name.lastIndexOf('/');
1245 if (index == -1) {
1246 cn = name;
1247 pn = "";
1248 } else {
1249 cn = name.replace('/', '.');
1250 pn = cn.substring(0, index);
1251 }
1252 if (!pn.equals(lookupClass.getPackageName())) {
1253 throw new IllegalArgumentException(cn + " not in same package as lookup class: " + lookupClass.getName());
1254 }
1255
1256 if ((flags & NONFINDABLE_CLASS) != 0) {
1257 // ## TODO use '/' as in the name of the VM anonymous class.
1258 cn = cn + '\\' + ++seq;
1259 }
1260
1261 // invoke the class loader's defineClass method
1262 ClassLoader loader = lookupClass.getClassLoader();
1263 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
1264 Class<?> clazz = JLA.defineClass(loader, lookupClass, cn, bytes, pd, flags, classData);
1265 assert clazz.getClassLoader() == lookupClass.getClassLoader()
1266 && clazz.getPackageName().equals(lookupClass.getPackageName());
1267
1268 // ## TBD what if multiple threads defining this same class??
1269 // may need VM to inject the classData in a Class itself at define class time
1270 if (classData != null) {
1271 CLASS_DATA_MAP.putIfAbsent(clazz, classData);
1272 }
1273 return clazz;
1274 }
1275
1276 private static volatile int seq = 0;
1277
1278 private ProtectionDomain lookupClassProtectionDomain() {
1279 ProtectionDomain pd = cachedProtectionDomain;
1280 if (pd == null) {
1281 cachedProtectionDomain = pd = JLA.protectionDomain(lookupClass);
1282 }
1283 return pd;
1284 }
1285
1286 // cached protection domain
1287 private volatile ProtectionDomain cachedProtectionDomain;
1288
1289 // don't see the need to use ClassValue
1290 private static final WeakHashMap<Class<?>, Object> CLASS_DATA_MAP = new WeakHashMap<>();
1291
1292 // Make sure outer class is initialized first.
1293 static { IMPL_NAMES.getClass(); }
1294
1295 /** Package-private version of lookup which is trusted. */
1296 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
1297
1298 /** Version of lookup which is trusted minimally.
1299 * It can only be used to create method handles to publicly accessible
1300 * members in packages that are exported unconditionally.
1301 */
1302 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
1303
1304 static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
1305
1306 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
1307 String name = lookupClass.getName();
1308 if (name.startsWith("java.lang.invoke."))
1309 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1310 }
1311
1312 /**
1313 * Displays the name of the class from which lookups are to be made.
1314 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1315 * If there are restrictions on the access permitted to this lookup,
1316 * this is indicated by adding a suffix to the class name, consisting
1317 * of a slash and a keyword. The keyword represents the strongest
1318 * allowed access, and is chosen as follows:
1319 * <ul>
1320 * <li>If no access is allowed, the suffix is "/noaccess".
1321 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1322 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1323 * <li>If only public and module access are allowed, the suffix is "/module".
1324 * <li>If only public, module and package access are allowed, the suffix is "/package".
1325 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1326 * </ul>
1327 * If none of the above cases apply, it is the case that full
1328 * access (public, module, package, private, and protected) is allowed.
1329 * In this case, no suffix is added.
1330 * This is true only of an object obtained originally from
1331 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1332 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1333 * always have restricted access, and will display a suffix.
1334 * <p>
1335 * (It may seem strange that protected access should be
1336 * stronger than private access. Viewed independently from
1337 * package access, protected access is the first to be lost,
1338 * because it requires a direct subclass relationship between
1339 * caller and callee.)
1340 * @see #in
1341 *
1342 * @revised 9
1343 * @spec JPMS
1344 */
1345 @Override
1346 public String toString() {
1347 String cname = lookupClass.getName();
1348 switch (allowedModes) {
1349 case 0: // no privileges
1350 return cname + "/noaccess";
1351 case PUBLIC:
1352 return cname + "/public";
1353 case PUBLIC|UNCONDITIONAL:
1354 return cname + "/publicLookup";
1355 case PUBLIC|MODULE:
1356 return cname + "/module";
1357 case PUBLIC|MODULE|PACKAGE:
1358 return cname + "/package";
1359 case FULL_POWER_MODES & ~PROTECTED:
1360 return cname + "/private";
1361 case FULL_POWER_MODES:
1362 return cname;
1363 case TRUSTED:
1364 return "/trusted"; // internal only; not exported
1365 default: // Should not happen, but it's a bitfield...
1366 cname = cname + "/" + Integer.toHexString(allowedModes);
1367 assert(false) : cname;
1368 return cname;
1369 }
1370 }
1371
1372 /**
1373 * Produces a method handle for a static method.
1374 * The type of the method handle will be that of the method.
1375 * (Since static methods do not take receivers, there is no
1376 * additional receiver argument inserted into the method handle type,
1377 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1378 * The method and all its argument types must be accessible to the lookup object.
1379 * <p>
1380 * The returned method handle will have
1381 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1382 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1383 * <p>
1384 * If the returned method handle is invoked, the method's class will
1385 * be initialized, if it has not already been initialized.
1386 * <p><b>Example:</b>
1387 * <blockquote><pre>{@code
1388 import static java.lang.invoke.MethodHandles.*;
1389 import static java.lang.invoke.MethodType.*;
1390 ...
1391 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1392 "asList", methodType(List.class, Object[].class));
1393 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1394 * }</pre></blockquote>
1395 * @param refc the class from which the method is accessed
1396 * @param name the name of the method
1397 * @param type the type of the method
1398 * @return the desired method handle
1399 * @throws NoSuchMethodException if the method does not exist
1400 * @throws IllegalAccessException if access checking fails,
1401 * or if the method is not {@code static},
1402 * or if the method's variable arity modifier bit
1403 * is set and {@code asVarargsCollector} fails
1404 * @exception SecurityException if a security manager is present and it
1405 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1406 * @throws NullPointerException if any argument is null
1407 */
1408 public
1409 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1410 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1411 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1412 }
1413
1414 /**
1415 * Produces a method handle for a virtual method.
1416 * The type of the method handle will be that of the method,
1417 * with the receiver type (usually {@code refc}) prepended.
1418 * The method and all its argument types must be accessible to the lookup object.
1419 * <p>
1420 * When called, the handle will treat the first argument as a receiver
1421 * and, for non-private methods, dispatch on the receiver's type to determine which method
1422 * implementation to enter.
1423 * For private methods the named method in {@code refc} will be invoked on the receiver.
1424 * (The dispatching action is identical with that performed by an
1425 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1426 * <p>
1427 * The first argument will be of type {@code refc} if the lookup
1428 * class has full privileges to access the member. Otherwise
1429 * the member must be {@code protected} and the first argument
1430 * will be restricted in type to the lookup class.
1431 * <p>
1432 * The returned method handle will have
1433 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1434 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1435 * <p>
1436 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1437 * instructions and method handles produced by {@code findVirtual},
1438 * if the class is {@code MethodHandle} and the name string is
1439 * {@code invokeExact} or {@code invoke}, the resulting
1440 * method handle is equivalent to one produced by
1441 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1442 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1443 * with the same {@code type} argument.
1444 * <p>
1445 * If the class is {@code VarHandle} and the name string corresponds to
1446 * the name of a signature-polymorphic access mode method, the resulting
1447 * method handle is equivalent to one produced by
1448 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1449 * the access mode corresponding to the name string and with the same
1450 * {@code type} arguments.
1451 * <p>
1452 * <b>Example:</b>
1453 * <blockquote><pre>{@code
1454 import static java.lang.invoke.MethodHandles.*;
1455 import static java.lang.invoke.MethodType.*;
1456 ...
1457 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1458 "concat", methodType(String.class, String.class));
1459 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1460 "hashCode", methodType(int.class));
1461 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1462 "hashCode", methodType(int.class));
1463 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1464 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1465 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1466 // interface method:
1467 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1468 "subSequence", methodType(CharSequence.class, int.class, int.class));
1469 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1470 // constructor "internal method" must be accessed differently:
1471 MethodType MT_newString = methodType(void.class); //()V for new String()
1472 try { assertEquals("impossible", lookup()
1473 .findVirtual(String.class, "<init>", MT_newString));
1474 } catch (NoSuchMethodException ex) { } // OK
1475 MethodHandle MH_newString = publicLookup()
1476 .findConstructor(String.class, MT_newString);
1477 assertEquals("", (String) MH_newString.invokeExact());
1478 * }</pre></blockquote>
1479 *
1480 * @param refc the class or interface from which the method is accessed
1481 * @param name the name of the method
1482 * @param type the type of the method, with the receiver argument omitted
1483 * @return the desired method handle
1484 * @throws NoSuchMethodException if the method does not exist
1485 * @throws IllegalAccessException if access checking fails,
1486 * or if the method is {@code static},
1487 * or if the method's variable arity modifier bit
1488 * is set and {@code asVarargsCollector} fails
1489 * @exception SecurityException if a security manager is present and it
1490 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1491 * @throws NullPointerException if any argument is null
1492 */
1493 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1494 if (refc == MethodHandle.class) {
1495 MethodHandle mh = findVirtualForMH(name, type);
1496 if (mh != null) return mh;
1497 } else if (refc == VarHandle.class) {
1498 MethodHandle mh = findVirtualForVH(name, type);
1499 if (mh != null) return mh;
1500 }
1501 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1502 MemberName method = resolveOrFail(refKind, refc, name, type);
1503 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1504 }
1505 private MethodHandle findVirtualForMH(String name, MethodType type) {
1506 // these names require special lookups because of the implicit MethodType argument
1507 if ("invoke".equals(name))
1508 return invoker(type);
1509 if ("invokeExact".equals(name))
1510 return exactInvoker(type);
1511 assert(!MemberName.isMethodHandleInvokeName(name));
1512 return null;
1513 }
1514 private MethodHandle findVirtualForVH(String name, MethodType type) {
1515 try {
1516 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1517 } catch (IllegalArgumentException e) {
1518 return null;
1519 }
1520 }
1521
1522 /**
1523 * Produces a method handle which creates an object and initializes it, using
1524 * the constructor of the specified type.
1525 * The parameter types of the method handle will be those of the constructor,
1526 * while the return type will be a reference to the constructor's class.
1527 * The constructor and all its argument types must be accessible to the lookup object.
1528 * <p>
1529 * The requested type must have a return type of {@code void}.
1530 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1531 * <p>
1532 * The returned method handle will have
1533 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1534 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1535 * <p>
1536 * If the returned method handle is invoked, the constructor's class will
1537 * be initialized, if it has not already been initialized.
1538 * <p><b>Example:</b>
1539 * <blockquote><pre>{@code
1540 import static java.lang.invoke.MethodHandles.*;
1541 import static java.lang.invoke.MethodType.*;
1542 ...
1543 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1544 ArrayList.class, methodType(void.class, Collection.class));
1545 Collection orig = Arrays.asList("x", "y");
1546 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1547 assert(orig != copy);
1548 assertEquals(orig, copy);
1549 // a variable-arity constructor:
1550 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1551 ProcessBuilder.class, methodType(void.class, String[].class));
1552 ProcessBuilder pb = (ProcessBuilder)
1553 MH_newProcessBuilder.invoke("x", "y", "z");
1554 assertEquals("[x, y, z]", pb.command().toString());
1555 * }</pre></blockquote>
1556 * @param refc the class or interface from which the method is accessed
1557 * @param type the type of the method, with the receiver argument omitted, and a void return type
1558 * @return the desired method handle
1559 * @throws NoSuchMethodException if the constructor does not exist
1560 * @throws IllegalAccessException if access checking fails
1561 * or if the method's variable arity modifier bit
1562 * is set and {@code asVarargsCollector} fails
1563 * @exception SecurityException if a security manager is present and it
1564 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1565 * @throws NullPointerException if any argument is null
1566 */
1567 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1568 if (refc.isArray()) {
1569 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1570 }
1571 String name = "<init>";
1572 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1573 return getDirectConstructor(refc, ctor);
1574 }
1575
1576 /**
1577 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1578 * initializer of the class is not run.
1579 * <p>
1580 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1581 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1582 * load the requested class, and then determines whether the class is accessible to this lookup object.
1583 *
1584 * @param targetName the fully qualified name of the class to be looked up.
1585 * @return the requested class.
1586 * @exception SecurityException if a security manager is present and it
1587 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1588 * @throws LinkageError if the linkage fails
1589 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader
1590 * or the class is not {@linkplain Class#isHidden hidden}
1591 * @throws IllegalAccessException if the class is not accessible, using the allowed access modes.
1592
1593 * @since 9
1594 * @see Class#isHidden
1595 */
1596 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1597 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1598 return accessClass(targetClass);
1599 }
1600
1601 /**
1602 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1603 * static initializer of the class is not run.
1604 * <p>
1605 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1606 * {@linkplain #lookupModes() lookup modes}.
1607 *
1608 * @param targetClass the class to be access-checked
1609 *
1610 * @return the class that has been access-checked
1611 *
1612 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1613 * modes.
1614 * @exception SecurityException if a security manager is present and it
1615 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1616 * @since 9
1617 */
1618 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1619 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1620 throw new MemberName(targetClass).makeAccessException("access violation", this);
1621 }
1622 checkSecurityManager(targetClass, null);
1623 return targetClass;
1624 }
1625
1626 /**
1627 * Produces an early-bound method handle for a virtual method.
1628 * It will bypass checks for overriding methods on the receiver,
1629 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1630 * instruction from within the explicitly specified {@code specialCaller}.
1631 * The type of the method handle will be that of the method,
1632 * with a suitably restricted receiver type prepended.
1633 * (The receiver type will be {@code specialCaller} or a subtype.)
1634 * The method and all its argument types must be accessible
1635 * to the lookup object.
1636 * <p>
1637 * Before method resolution,
1638 * if the explicitly specified caller class is not identical with the
1639 * lookup class, or if this lookup object does not have
1640 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1641 * privileges, the access fails.
1642 * <p>
1643 * The returned method handle will have
1644 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1645 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1646 * <p style="font-size:smaller;">
1647 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1648 * even though the {@code invokespecial} instruction can refer to them
1649 * in special circumstances. Use {@link #findConstructor findConstructor}
1650 * to access instance initialization methods in a safe manner.)</em>
1651 * <p><b>Example:</b>
1652 * <blockquote><pre>{@code
1653 import static java.lang.invoke.MethodHandles.*;
1654 import static java.lang.invoke.MethodType.*;
1655 ...
1656 static class Listie extends ArrayList {
1657 public String toString() { return "[wee Listie]"; }
1658 static Lookup lookup() { return MethodHandles.lookup(); }
1659 }
1660 ...
1661 // no access to constructor via invokeSpecial:
1662 MethodHandle MH_newListie = Listie.lookup()
1663 .findConstructor(Listie.class, methodType(void.class));
1664 Listie l = (Listie) MH_newListie.invokeExact();
1665 try { assertEquals("impossible", Listie.lookup().findSpecial(
1666 Listie.class, "<init>", methodType(void.class), Listie.class));
1667 } catch (NoSuchMethodException ex) { } // OK
1668 // access to super and self methods via invokeSpecial:
1669 MethodHandle MH_super = Listie.lookup().findSpecial(
1670 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1671 MethodHandle MH_this = Listie.lookup().findSpecial(
1672 Listie.class, "toString" , methodType(String.class), Listie.class);
1673 MethodHandle MH_duper = Listie.lookup().findSpecial(
1674 Object.class, "toString" , methodType(String.class), Listie.class);
1675 assertEquals("[]", (String) MH_super.invokeExact(l));
1676 assertEquals(""+l, (String) MH_this.invokeExact(l));
1677 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1678 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1679 String.class, "toString", methodType(String.class), Listie.class));
1680 } catch (IllegalAccessException ex) { } // OK
1681 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1682 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1683 * }</pre></blockquote>
1684 *
1685 * @param refc the class or interface from which the method is accessed
1686 * @param name the name of the method (which must not be "<init>")
1687 * @param type the type of the method, with the receiver argument omitted
1688 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1689 * @return the desired method handle
1690 * @throws NoSuchMethodException if the method does not exist
1691 * @throws IllegalAccessException if access checking fails,
1692 * or if the method is {@code static},
1693 * or if the method's variable arity modifier bit
1694 * is set and {@code asVarargsCollector} fails
1695 * @exception SecurityException if a security manager is present and it
1696 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1697 * @throws NullPointerException if any argument is null
1698 */
1699 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1700 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1701 checkSpecialCaller(specialCaller, refc);
1702 Lookup specialLookup = this.in(specialCaller);
1703 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1704 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1705 }
1706
1707 /**
1708 * Produces a method handle giving read access to a non-static field.
1709 * The type of the method handle will have a return type of the field's
1710 * value type.
1711 * The method handle's single argument will be the instance containing
1712 * the field.
1713 * Access checking is performed immediately on behalf of the lookup class.
1714 * @param refc the class or interface from which the method is accessed
1715 * @param name the field's name
1716 * @param type the field's type
1717 * @return a method handle which can load values from the field
1718 * @throws NoSuchFieldException if the field does not exist
1719 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1720 * @exception SecurityException if a security manager is present and it
1721 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1722 * @throws NullPointerException if any argument is null
1723 * @see #findVarHandle(Class, String, Class)
1724 */
1725 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1726 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1727 return getDirectField(REF_getField, refc, field);
1728 }
1729
1730 /**
1731 * Produces a method handle giving write access to a non-static field.
1732 * The type of the method handle will have a void return type.
1733 * The method handle will take two arguments, the instance containing
1734 * the field, and the value to be stored.
1735 * The second argument will be of the field's value type.
1736 * Access checking is performed immediately on behalf of the lookup class.
1737 * @param refc the class or interface from which the method is accessed
1738 * @param name the field's name
1739 * @param type the field's type
1740 * @return a method handle which can store values into the field
1741 * @throws NoSuchFieldException if the field does not exist
1742 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1743 * @exception SecurityException if a security manager is present and it
1744 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1745 * @throws NullPointerException if any argument is null
1746 * @see #findVarHandle(Class, String, Class)
1747 */
1748 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1749 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1750 return getDirectField(REF_putField, refc, field);
1751 }
1752
1753 /**
1754 * Produces a VarHandle giving access to a non-static field {@code name}
1755 * of type {@code type} declared in a class of type {@code recv}.
1756 * The VarHandle's variable type is {@code type} and it has one
1757 * coordinate type, {@code recv}.
1758 * <p>
1759 * Access checking is performed immediately on behalf of the lookup
1760 * class.
1761 * <p>
1762 * Certain access modes of the returned VarHandle are unsupported under
1763 * the following conditions:
1764 * <ul>
1765 * <li>if the field is declared {@code final}, then the write, atomic
1766 * update, numeric atomic update, and bitwise atomic update access
1767 * modes are unsupported.
1768 * <li>if the field type is anything other than {@code byte},
1769 * {@code short}, {@code char}, {@code int}, {@code long},
1770 * {@code float}, or {@code double} then numeric atomic update
1771 * access modes are unsupported.
1772 * <li>if the field type is anything other than {@code boolean},
1773 * {@code byte}, {@code short}, {@code char}, {@code int} or
1774 * {@code long} then bitwise atomic update access modes are
1775 * unsupported.
1776 * </ul>
1777 * <p>
1778 * If the field is declared {@code volatile} then the returned VarHandle
1779 * will override access to the field (effectively ignore the
1780 * {@code volatile} declaration) in accordance to its specified
1781 * access modes.
1782 * <p>
1783 * If the field type is {@code float} or {@code double} then numeric
1784 * and atomic update access modes compare values using their bitwise
1785 * representation (see {@link Float#floatToRawIntBits} and
1786 * {@link Double#doubleToRawLongBits}, respectively).
1787 * @apiNote
1788 * Bitwise comparison of {@code float} values or {@code double} values,
1789 * as performed by the numeric and atomic update access modes, differ
1790 * from the primitive {@code ==} operator and the {@link Float#equals}
1791 * and {@link Double#equals} methods, specifically with respect to
1792 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1793 * Care should be taken when performing a compare and set or a compare
1794 * and exchange operation with such values since the operation may
1795 * unexpectedly fail.
1796 * There are many possible NaN values that are considered to be
1797 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1798 * provided by Java can distinguish between them. Operation failure can
1799 * occur if the expected or witness value is a NaN value and it is
1800 * transformed (perhaps in a platform specific manner) into another NaN
1801 * value, and thus has a different bitwise representation (see
1802 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1803 * details).
1804 * The values {@code -0.0} and {@code +0.0} have different bitwise
1805 * representations but are considered equal when using the primitive
1806 * {@code ==} operator. Operation failure can occur if, for example, a
1807 * numeric algorithm computes an expected value to be say {@code -0.0}
1808 * and previously computed the witness value to be say {@code +0.0}.
1809 * @param recv the receiver class, of type {@code R}, that declares the
1810 * non-static field
1811 * @param name the field's name
1812 * @param type the field's type, of type {@code T}
1813 * @return a VarHandle giving access to non-static fields.
1814 * @throws NoSuchFieldException if the field does not exist
1815 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1816 * @exception SecurityException if a security manager is present and it
1817 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1818 * @throws NullPointerException if any argument is null
1819 * @since 9
1820 */
1821 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1822 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1823 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1824 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1825 }
1826
1827 /**
1828 * Produces a method handle giving read access to a static field.
1829 * The type of the method handle will have a return type of the field's
1830 * value type.
1831 * The method handle will take no arguments.
1832 * Access checking is performed immediately on behalf of the lookup class.
1833 * <p>
1834 * If the returned method handle is invoked, the field's class will
1835 * be initialized, if it has not already been initialized.
1836 * @param refc the class or interface from which the method is accessed
1837 * @param name the field's name
1838 * @param type the field's type
1839 * @return a method handle which can load values from the field
1840 * @throws NoSuchFieldException if the field does not exist
1841 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1842 * @exception SecurityException if a security manager is present and it
1843 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1844 * @throws NullPointerException if any argument is null
1845 */
1846 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1847 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1848 return getDirectField(REF_getStatic, refc, field);
1849 }
1850
1851 /**
1852 * Produces a method handle giving write access to a static field.
1853 * The type of the method handle will have a void return type.
1854 * The method handle will take a single
1855 * argument, of the field's value type, the value to be stored.
1856 * Access checking is performed immediately on behalf of the lookup class.
1857 * <p>
1858 * If the returned method handle is invoked, the field's class will
1859 * be initialized, if it has not already been initialized.
1860 * @param refc the class or interface from which the method is accessed
1861 * @param name the field's name
1862 * @param type the field's type
1863 * @return a method handle which can store values into the field
1864 * @throws NoSuchFieldException if the field does not exist
1865 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1866 * @exception SecurityException if a security manager is present and it
1867 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1868 * @throws NullPointerException if any argument is null
1869 */
1870 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1871 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1872 return getDirectField(REF_putStatic, refc, field);
1873 }
1874
1875 /**
1876 * Produces a VarHandle giving access to a static field {@code name} of
1877 * type {@code type} declared in a class of type {@code decl}.
1878 * The VarHandle's variable type is {@code type} and it has no
1879 * coordinate types.
1880 * <p>
1881 * Access checking is performed immediately on behalf of the lookup
1882 * class.
1883 * <p>
1884 * If the returned VarHandle is operated on, the declaring class will be
1885 * initialized, if it has not already been initialized.
1886 * <p>
1887 * Certain access modes of the returned VarHandle are unsupported under
1888 * the following conditions:
1889 * <ul>
1890 * <li>if the field is declared {@code final}, then the write, atomic
1891 * update, numeric atomic update, and bitwise atomic update access
1892 * modes are unsupported.
1893 * <li>if the field type is anything other than {@code byte},
1894 * {@code short}, {@code char}, {@code int}, {@code long},
1895 * {@code float}, or {@code double}, then numeric atomic update
1896 * access modes are unsupported.
1897 * <li>if the field type is anything other than {@code boolean},
1898 * {@code byte}, {@code short}, {@code char}, {@code int} or
1899 * {@code long} then bitwise atomic update access modes are
1900 * unsupported.
1901 * </ul>
1902 * <p>
1903 * If the field is declared {@code volatile} then the returned VarHandle
1904 * will override access to the field (effectively ignore the
1905 * {@code volatile} declaration) in accordance to its specified
1906 * access modes.
1907 * <p>
1908 * If the field type is {@code float} or {@code double} then numeric
1909 * and atomic update access modes compare values using their bitwise
1910 * representation (see {@link Float#floatToRawIntBits} and
1911 * {@link Double#doubleToRawLongBits}, respectively).
1912 * @apiNote
1913 * Bitwise comparison of {@code float} values or {@code double} values,
1914 * as performed by the numeric and atomic update access modes, differ
1915 * from the primitive {@code ==} operator and the {@link Float#equals}
1916 * and {@link Double#equals} methods, specifically with respect to
1917 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1918 * Care should be taken when performing a compare and set or a compare
1919 * and exchange operation with such values since the operation may
1920 * unexpectedly fail.
1921 * There are many possible NaN values that are considered to be
1922 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1923 * provided by Java can distinguish between them. Operation failure can
1924 * occur if the expected or witness value is a NaN value and it is
1925 * transformed (perhaps in a platform specific manner) into another NaN
1926 * value, and thus has a different bitwise representation (see
1927 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1928 * details).
1929 * The values {@code -0.0} and {@code +0.0} have different bitwise
1930 * representations but are considered equal when using the primitive
1931 * {@code ==} operator. Operation failure can occur if, for example, a
1932 * numeric algorithm computes an expected value to be say {@code -0.0}
1933 * and previously computed the witness value to be say {@code +0.0}.
1934 * @param decl the class that declares the static field
1935 * @param name the field's name
1936 * @param type the field's type, of type {@code T}
1937 * @return a VarHandle giving access to a static field
1938 * @throws NoSuchFieldException if the field does not exist
1939 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1940 * @exception SecurityException if a security manager is present and it
1941 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1942 * @throws NullPointerException if any argument is null
1943 * @since 9
1944 */
1945 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1946 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1947 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1948 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1949 }
1950
1951 /**
1952 * Produces an early-bound method handle for a non-static method.
1953 * The receiver must have a supertype {@code defc} in which a method
1954 * of the given name and type is accessible to the lookup class.
1955 * The method and all its argument types must be accessible to the lookup object.
1956 * The type of the method handle will be that of the method,
1957 * without any insertion of an additional receiver parameter.
1958 * The given receiver will be bound into the method handle,
1959 * so that every call to the method handle will invoke the
1960 * requested method on the given receiver.
1961 * <p>
1962 * The returned method handle will have
1963 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1964 * the method's variable arity modifier bit ({@code 0x0080}) is set
1965 * <em>and</em> the trailing array argument is not the only argument.
1966 * (If the trailing array argument is the only argument,
1967 * the given receiver value will be bound to it.)
1968 * <p>
1969 * This is almost equivalent to the following code, with some differences noted below:
1970 * <blockquote><pre>{@code
1971 import static java.lang.invoke.MethodHandles.*;
1972 import static java.lang.invoke.MethodType.*;
1973 ...
1974 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1975 MethodHandle mh1 = mh0.bindTo(receiver);
1976 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1977 return mh1;
1978 * }</pre></blockquote>
1979 * where {@code defc} is either {@code receiver.getClass()} or a super
1980 * type of that class, in which the requested method is accessible
1981 * to the lookup class.
1982 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1983 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1984 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1985 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1986 * @param receiver the object from which the method is accessed
1987 * @param name the name of the method
1988 * @param type the type of the method, with the receiver argument omitted
1989 * @return the desired method handle
1990 * @throws NoSuchMethodException if the method does not exist
1991 * @throws IllegalAccessException if access checking fails
1992 * or if the method's variable arity modifier bit
1993 * is set and {@code asVarargsCollector} fails
1994 * @exception SecurityException if a security manager is present and it
1995 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1996 * @throws NullPointerException if any argument is null
1997 * @see MethodHandle#bindTo
1998 * @see #findVirtual
1999 */
2000 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2001 Class<? extends Object> refc = receiver.getClass(); // may get NPE
2002 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
2003 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
2004 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
2005 throw new IllegalAccessException("The restricted defining class " +
2006 mh.type().leadingReferenceParameter().getName() +
2007 " is not assignable from receiver class " +
2008 receiver.getClass().getName());
2009 }
2010 return mh.bindArgumentL(0, receiver).setVarargs(method);
2011 }
2012
2013 /**
2014 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2015 * to <i>m</i>, if the lookup class has permission.
2016 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
2017 * If <i>m</i> is virtual, overriding is respected on every call.
2018 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
2019 * The type of the method handle will be that of the method,
2020 * with the receiver type prepended (but only if it is non-static).
2021 * If the method's {@code accessible} flag is not set,
2022 * access checking is performed immediately on behalf of the lookup class.
2023 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
2024 * <p>
2025 * The returned method handle will have
2026 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2027 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2028 * <p>
2029 * If <i>m</i> is static, and
2030 * if the returned method handle is invoked, the method's class will
2031 * be initialized, if it has not already been initialized.
2032 * @param m the reflected method
2033 * @return a method handle which can invoke the reflected method
2034 * @throws IllegalAccessException if access checking fails
2035 * or if the method's variable arity modifier bit
2036 * is set and {@code asVarargsCollector} fails
2037 * @throws NullPointerException if the argument is null
2038 */
2039 public MethodHandle unreflect(Method m) throws IllegalAccessException {
2040 if (m.getDeclaringClass() == MethodHandle.class) {
2041 MethodHandle mh = unreflectForMH(m);
2042 if (mh != null) return mh;
2043 }
2044 if (m.getDeclaringClass() == VarHandle.class) {
2045 MethodHandle mh = unreflectForVH(m);
2046 if (mh != null) return mh;
2047 }
2048 MemberName method = new MemberName(m);
2049 byte refKind = method.getReferenceKind();
2050 if (refKind == REF_invokeSpecial)
2051 refKind = REF_invokeVirtual;
2052 assert(method.isMethod());
2053 @SuppressWarnings("deprecation")
2054 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
2055 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
2056 }
2057 private MethodHandle unreflectForMH(Method m) {
2058 // these names require special lookups because they throw UnsupportedOperationException
2059 if (MemberName.isMethodHandleInvokeName(m.getName()))
2060 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
2061 return null;
2062 }
2063 private MethodHandle unreflectForVH(Method m) {
2064 // these names require special lookups because they throw UnsupportedOperationException
2065 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
2066 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
2067 return null;
2068 }
2069
2070 /**
2071 * Produces a method handle for a reflected method.
2072 * It will bypass checks for overriding methods on the receiver,
2073 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2074 * instruction from within the explicitly specified {@code specialCaller}.
2075 * The type of the method handle will be that of the method,
2076 * with a suitably restricted receiver type prepended.
2077 * (The receiver type will be {@code specialCaller} or a subtype.)
2078 * If the method's {@code accessible} flag is not set,
2079 * access checking is performed immediately on behalf of the lookup class,
2080 * as if {@code invokespecial} instruction were being linked.
2081 * <p>
2082 * Before method resolution,
2083 * if the explicitly specified caller class is not identical with the
2084 * lookup class, or if this lookup object does not have
2085 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2086 * privileges, the access fails.
2087 * <p>
2088 * The returned method handle will have
2089 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2090 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2091 * @param m the reflected method
2092 * @param specialCaller the class nominally calling the method
2093 * @return a method handle which can invoke the reflected method
2094 * @throws IllegalAccessException if access checking fails,
2095 * or if the method is {@code static},
2096 * or if the method's variable arity modifier bit
2097 * is set and {@code asVarargsCollector} fails
2098 * @throws NullPointerException if any argument is null
2099 */
2100 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
2101 checkSpecialCaller(specialCaller, null);
2102 Lookup specialLookup = this.in(specialCaller);
2103 MemberName method = new MemberName(m, true);
2104 assert(method.isMethod());
2105 // ignore m.isAccessible: this is a new kind of access
2106 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
2107 }
2108
2109 /**
2110 * Produces a method handle for a reflected constructor.
2111 * The type of the method handle will be that of the constructor,
2112 * with the return type changed to the declaring class.
2113 * The method handle will perform a {@code newInstance} operation,
2114 * creating a new instance of the constructor's class on the
2115 * arguments passed to the method handle.
2116 * <p>
2117 * If the constructor's {@code accessible} flag is not set,
2118 * access checking is performed immediately on behalf of the lookup class.
2119 * <p>
2120 * The returned method handle will have
2121 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2122 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2123 * <p>
2124 * If the returned method handle is invoked, the constructor's class will
2125 * be initialized, if it has not already been initialized.
2126 * @param c the reflected constructor
2127 * @return a method handle which can invoke the reflected constructor
2128 * @throws IllegalAccessException if access checking fails
2129 * or if the method's variable arity modifier bit
2130 * is set and {@code asVarargsCollector} fails
2131 * @throws NullPointerException if the argument is null
2132 */
2133 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
2134 MemberName ctor = new MemberName(c);
2135 assert(ctor.isConstructor());
2136 @SuppressWarnings("deprecation")
2137 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
2138 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
2139 }
2140
2141 /**
2142 * Produces a method handle giving read access to a reflected field.
2143 * The type of the method handle will have a return type of the field's
2144 * value type.
2145 * If the field is static, the method handle will take no arguments.
2146 * Otherwise, its single argument will be the instance containing
2147 * the field.
2148 * If the field's {@code accessible} flag is not set,
2149 * access checking is performed immediately on behalf of the lookup class.
2150 * <p>
2151 * If the field is static, and
2152 * if the returned method handle is invoked, the field's class will
2153 * be initialized, if it has not already been initialized.
2154 * @param f the reflected field
2155 * @return a method handle which can load values from the reflected field
2156 * @throws IllegalAccessException if access checking fails
2157 * @throws NullPointerException if the argument is null
2158 */
2159 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
2160 return unreflectField(f, false);
2161 }
2162 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
2163 MemberName field = new MemberName(f, isSetter);
2164 assert(isSetter
2165 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
2166 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
2167 @SuppressWarnings("deprecation")
2168 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
2169 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
2170 }
2171
2172 /**
2173 * Produces a method handle giving write access to a reflected field.
2174 * The type of the method handle will have a void return type.
2175 * If the field is static, the method handle will take a single
2176 * argument, of the field's value type, the value to be stored.
2177 * Otherwise, the two arguments will be the instance containing
2178 * the field, and the value to be stored.
2179 * If the field's {@code accessible} flag is not set,
2180 * access checking is performed immediately on behalf of the lookup class.
2181 * <p>
2182 * If the field is static, and
2183 * if the returned method handle is invoked, the field's class will
2184 * be initialized, if it has not already been initialized.
2185 * @param f the reflected field
2186 * @return a method handle which can store values into the reflected field
2187 * @throws IllegalAccessException if access checking fails
2188 * @throws NullPointerException if the argument is null
2189 */
2190 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
2191 return unreflectField(f, true);
2192 }
2193
2194 /**
2195 * Produces a VarHandle giving access to a reflected field {@code f}
2196 * of type {@code T} declared in a class of type {@code R}.
2197 * The VarHandle's variable type is {@code T}.
2198 * If the field is non-static the VarHandle has one coordinate type,
2199 * {@code R}. Otherwise, the field is static, and the VarHandle has no
2200 * coordinate types.
2201 * <p>
2202 * Access checking is performed immediately on behalf of the lookup
2203 * class, regardless of the value of the field's {@code accessible}
2204 * flag.
2205 * <p>
2206 * If the field is static, and if the returned VarHandle is operated
2207 * on, the field's declaring class will be initialized, if it has not
2208 * already been initialized.
2209 * <p>
2210 * Certain access modes of the returned VarHandle are unsupported under
2211 * the following conditions:
2212 * <ul>
2213 * <li>if the field is declared {@code final}, then the write, atomic
2214 * update, numeric atomic update, and bitwise atomic update access
2215 * modes are unsupported.
2216 * <li>if the field type is anything other than {@code byte},
2217 * {@code short}, {@code char}, {@code int}, {@code long},
2218 * {@code float}, or {@code double} then numeric atomic update
2219 * access modes are unsupported.
2220 * <li>if the field type is anything other than {@code boolean},
2221 * {@code byte}, {@code short}, {@code char}, {@code int} or
2222 * {@code long} then bitwise atomic update access modes are
2223 * unsupported.
2224 * </ul>
2225 * <p>
2226 * If the field is declared {@code volatile} then the returned VarHandle
2227 * will override access to the field (effectively ignore the
2228 * {@code volatile} declaration) in accordance to its specified
2229 * access modes.
2230 * <p>
2231 * If the field type is {@code float} or {@code double} then numeric
2232 * and atomic update access modes compare values using their bitwise
2233 * representation (see {@link Float#floatToRawIntBits} and
2234 * {@link Double#doubleToRawLongBits}, respectively).
2235 * @apiNote
2236 * Bitwise comparison of {@code float} values or {@code double} values,
2237 * as performed by the numeric and atomic update access modes, differ
2238 * from the primitive {@code ==} operator and the {@link Float#equals}
2239 * and {@link Double#equals} methods, specifically with respect to
2240 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2241 * Care should be taken when performing a compare and set or a compare
2242 * and exchange operation with such values since the operation may
2243 * unexpectedly fail.
2244 * There are many possible NaN values that are considered to be
2245 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2246 * provided by Java can distinguish between them. Operation failure can
2247 * occur if the expected or witness value is a NaN value and it is
2248 * transformed (perhaps in a platform specific manner) into another NaN
2249 * value, and thus has a different bitwise representation (see
2250 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2251 * details).
2252 * The values {@code -0.0} and {@code +0.0} have different bitwise
2253 * representations but are considered equal when using the primitive
2254 * {@code ==} operator. Operation failure can occur if, for example, a
2255 * numeric algorithm computes an expected value to be say {@code -0.0}
2256 * and previously computed the witness value to be say {@code +0.0}.
2257 * @param f the reflected field, with a field of type {@code T}, and
2258 * a declaring class of type {@code R}
2259 * @return a VarHandle giving access to non-static fields or a static
2260 * field
2261 * @throws IllegalAccessException if access checking fails
2262 * @throws NullPointerException if the argument is null
2263 * @since 9
2264 */
2265 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
2266 MemberName getField = new MemberName(f, false);
2267 MemberName putField = new MemberName(f, true);
2268 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
2269 f.getDeclaringClass(), getField, putField);
2270 }
2271
2272 /**
2273 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
2274 * created by this lookup object or a similar one.
2275 * Security and access checks are performed to ensure that this lookup object
2276 * is capable of reproducing the target method handle.
2277 * This means that the cracking may fail if target is a direct method handle
2278 * but was created by an unrelated lookup object.
2279 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
2280 * and was created by a lookup object for a different class.
2281 * @param target a direct method handle to crack into symbolic reference components
2282 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
2283 * @exception SecurityException if a security manager is present and it
2284 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2285 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
2286 * @exception NullPointerException if the target is {@code null}
2287 * @see MethodHandleInfo
2288 * @since 1.8
2289 */
2290 public MethodHandleInfo revealDirect(MethodHandle target) {
2291 MemberName member = target.internalMemberName();
2292 if (member == null || (!member.isResolved() &&
2293 !member.isMethodHandleInvoke() &&
2294 !member.isVarHandleMethodInvoke()))
2295 throw newIllegalArgumentException("not a direct method handle");
2296 Class<?> defc = member.getDeclaringClass();
2297 byte refKind = member.getReferenceKind();
2298 assert(MethodHandleNatives.refKindIsValid(refKind));
2299 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2300 // Devirtualized method invocation is usually formally virtual.
2301 // To avoid creating extra MemberName objects for this common case,
2302 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2303 refKind = REF_invokeVirtual;
2304 if (refKind == REF_invokeVirtual && defc.isInterface())
2305 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2306 refKind = REF_invokeInterface;
2307 // Check SM permissions and member access before cracking.
2308 try {
2309 checkAccess(refKind, defc, member);
2310 checkSecurityManager(defc, member);
2311 } catch (IllegalAccessException ex) {
2312 throw new IllegalArgumentException(ex);
2313 }
2314 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2315 Class<?> callerClass = target.internalCallerClass();
2316 if (!hasPrivateAccess() || callerClass != lookupClass())
2317 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2318 }
2319 // Produce the handle to the results.
2320 return new InfoFromMemberName(this, member, refKind);
2321 }
2322
2323 /// Helper methods, all package-private.
2324
2325 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2326 checkSymbolicClass(refc); // do this before attempting to resolve
2327 Objects.requireNonNull(name);
2328 Objects.requireNonNull(type);
2329 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2330 NoSuchFieldException.class);
2331 }
2332
2333 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2334 checkSymbolicClass(refc); // do this before attempting to resolve
2335 Objects.requireNonNull(name);
2336 Objects.requireNonNull(type);
2337 checkMethodName(refKind, name); // NPE check on name
2338 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2339 NoSuchMethodException.class);
2340 }
2341
2342 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2343 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2344 Objects.requireNonNull(member.getName());
2345 Objects.requireNonNull(member.getType());
2346 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2347 ReflectiveOperationException.class);
2348 }
2349
2350 MemberName resolveOrNull(byte refKind, MemberName member) {
2351 // do this before attempting to resolve
2352 if (!isClassAccessible(member.getDeclaringClass())) {
2353 return null;
2354 }
2355 Objects.requireNonNull(member.getName());
2356 Objects.requireNonNull(member.getType());
2357 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull());
2358 }
2359
2360 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2361 if (!isClassAccessible(refc)) {
2362 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2363 }
2364 }
2365
2366 boolean isClassAccessible(Class<?> refc) {
2367 Objects.requireNonNull(refc);
2368 Class<?> caller = lookupClassOrNull();
2369 return caller == null || VerifyAccess.isClassAccessible(refc, caller, allowedModes);
2370 }
2371
2372 /** Check name for an illegal leading "<" character. */
2373 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2374 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2375 throw new NoSuchMethodException("illegal method name: "+name);
2376 }
2377
2378
2379 /**
2380 * Find my trustable caller class if m is a caller sensitive method.
2381 * If this lookup object has private access, then the caller class is the lookupClass.
2382 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2383 */
2384 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2385 Class<?> callerClass = null;
2386 if (MethodHandleNatives.isCallerSensitive(m)) {
2387 // Only lookups with private access are allowed to resolve caller-sensitive methods
2388 if (hasPrivateAccess()) {
2389 callerClass = lookupClass;
2390 } else {
2391 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2392 }
2393 }
2394 return callerClass;
2395 }
2396
2397 /**
2398 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2399 * @return {@code true} if this lookup has {@code PRIVATE} access.
2400 * @since 9
2401 */
2402 public boolean hasPrivateAccess() {
2403 return (allowedModes & PRIVATE) != 0;
2404 }
2405
2406 /**
2407 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2408 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2409 * If this lookup object has private access, then the caller class is the lookupClass.
2410 */
2411 void checkSecurityManager(Class<?> refc, MemberName m) {
2412 SecurityManager smgr = System.getSecurityManager();
2413 if (smgr == null) return;
2414 if (allowedModes == TRUSTED) return;
2415
2416 // Step 1:
2417 boolean fullPowerLookup = hasPrivateAccess();
2418 if (!fullPowerLookup ||
2419 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2420 ReflectUtil.checkPackageAccess(refc);
2421 }
2422
2423 if (m == null) { // findClass or accessClass
2424 // Step 2b:
2425 if (!fullPowerLookup) {
2426 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2427 }
2428 return;
2429 }
2430
2431 // Step 2a:
2432 if (m.isPublic()) return;
2433 if (!fullPowerLookup) {
2434 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2435 }
2436
2437 // Step 3:
2438 Class<?> defc = m.getDeclaringClass();
2439 if (!fullPowerLookup && defc != refc) {
2440 ReflectUtil.checkPackageAccess(defc);
2441 }
2442 }
2443
2444 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2445 boolean wantStatic = (refKind == REF_invokeStatic);
2446 String message;
2447 if (m.isConstructor())
2448 message = "expected a method, not a constructor";
2449 else if (!m.isMethod())
2450 message = "expected a method";
2451 else if (wantStatic != m.isStatic())
2452 message = wantStatic ? "expected a static method" : "expected a non-static method";
2453 else
2454 { checkAccess(refKind, refc, m); return; }
2455 throw m.makeAccessException(message, this);
2456 }
2457
2458 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2459 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2460 String message;
2461 if (wantStatic != m.isStatic())
2462 message = wantStatic ? "expected a static field" : "expected a non-static field";
2463 else
2464 { checkAccess(refKind, refc, m); return; }
2465 throw m.makeAccessException(message, this);
2466 }
2467
2468 /** Check public/protected/private bits on the symbolic reference class and its member. */
2469 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2470 assert(m.referenceKindIsConsistentWith(refKind) &&
2471 MethodHandleNatives.refKindIsValid(refKind) &&
2472 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2473 int allowedModes = this.allowedModes;
2474 if (allowedModes == TRUSTED) return;
2475 int mods = m.getModifiers();
2476 if (Modifier.isProtected(mods) &&
2477 refKind == REF_invokeVirtual &&
2478 m.getDeclaringClass() == Object.class &&
2479 m.getName().equals("clone") &&
2480 refc.isArray()) {
2481 // The JVM does this hack also.
2482 // (See ClassVerifier::verify_invoke_instructions
2483 // and LinkResolver::check_method_accessability.)
2484 // Because the JVM does not allow separate methods on array types,
2485 // there is no separate method for int[].clone.
2486 // All arrays simply inherit Object.clone.
2487 // But for access checking logic, we make Object.clone
2488 // (normally protected) appear to be public.
2489 // Later on, when the DirectMethodHandle is created,
2490 // its leading argument will be restricted to the
2491 // requested array type.
2492 // N.B. The return type is not adjusted, because
2493 // that is *not* the bytecode behavior.
2494 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2495 }
2496 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2497 // cannot "new" a protected ctor in a different package
2498 mods ^= Modifier.PROTECTED;
2499 }
2500 if (Modifier.isFinal(mods) &&
2501 MethodHandleNatives.refKindIsSetter(refKind))
2502 throw m.makeAccessException("unexpected set of a final field", this);
2503 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2504 if ((requestedModes & allowedModes) != 0) {
2505 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2506 mods, lookupClass(), allowedModes))
2507 return;
2508 } else {
2509 // Protected members can also be checked as if they were package-private.
2510 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2511 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2512 return;
2513 }
2514 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2515 }
2516
2517 String accessFailedMessage(Class<?> refc, MemberName m) {
2518 Class<?> defc = m.getDeclaringClass();
2519 int mods = m.getModifiers();
2520 // check the class first:
2521 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2522 (defc == refc ||
2523 Modifier.isPublic(refc.getModifiers())));
2524 if (!classOK && (allowedModes & PACKAGE) != 0) {
2525 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2526 (defc == refc ||
2527 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2528 }
2529 if (!classOK)
2530 return "class is not public";
2531 if (Modifier.isPublic(mods))
2532 return "access to public member failed"; // (how?, module not readable?)
2533 if (Modifier.isPrivate(mods))
2534 return "member is private";
2535 if (Modifier.isProtected(mods))
2536 return "member is protected";
2537 return "member is private to package";
2538 }
2539
2540 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2541 int allowedModes = this.allowedModes;
2542 if (allowedModes == TRUSTED) return;
2543 if (!hasPrivateAccess()
2544 || (specialCaller != lookupClass()
2545 // ensure non-abstract methods in superinterfaces can be special-invoked
2546 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
2547 throw new MemberName(specialCaller).
2548 makeAccessException("no private access for invokespecial", this);
2549 }
2550
2551 private boolean restrictProtectedReceiver(MemberName method) {
2552 // The accessing class only has the right to use a protected member
2553 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2554 if (!method.isProtected() || method.isStatic()
2555 || allowedModes == TRUSTED
2556 || method.getDeclaringClass() == lookupClass()
2557 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
2558 return false;
2559 return true;
2560 }
2561 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2562 assert(!method.isStatic());
2563 // receiver type of mh is too wide; narrow to caller
2564 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2565 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2566 }
2567 MethodType rawType = mh.type();
2568 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2569 MethodType narrowType = rawType.changeParameterType(0, caller);
2570 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2571 assert(mh.viewAsTypeChecks(narrowType, true));
2572 return mh.copyWith(narrowType, mh.form);
2573 }
2574
2575 /** Check access and get the requested method. */
2576 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2577 final boolean doRestrict = true;
2578 final boolean checkSecurity = true;
2579 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2580 }
2581 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2582 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2583 final boolean doRestrict = false;
2584 final boolean checkSecurity = true;
2585 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, boundCallerClass);
2586 }
2587 /** Check access and get the requested method, eliding security manager checks. */
2588 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> boundCallerClass) throws IllegalAccessException {
2589 final boolean doRestrict = true;
2590 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2591 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, boundCallerClass);
2592 }
2593 /** Common code for all methods; do not call directly except from immediately above. */
2594 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2595 boolean checkSecurity,
2596 boolean doRestrict, Class<?> boundCallerClass) throws IllegalAccessException {
2597
2598 checkMethod(refKind, refc, method);
2599 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2600 if (checkSecurity)
2601 checkSecurityManager(refc, method);
2602 assert(!method.isMethodHandleInvoke());
2603
2604 if (refKind == REF_invokeSpecial &&
2605 refc != lookupClass() &&
2606 !refc.isInterface() &&
2607 refc != lookupClass().getSuperclass() &&
2608 refc.isAssignableFrom(lookupClass())) {
2609 assert(!method.getName().equals("<init>")); // not this code path
2610
2611 // Per JVMS 6.5, desc. of invokespecial instruction:
2612 // If the method is in a superclass of the LC,
2613 // and if our original search was above LC.super,
2614 // repeat the search (symbolic lookup) from LC.super
2615 // and continue with the direct superclass of that class,
2616 // and so forth, until a match is found or no further superclasses exist.
2617 // FIXME: MemberName.resolve should handle this instead.
2618 Class<?> refcAsSuper = lookupClass();
2619 MemberName m2;
2620 do {
2621 refcAsSuper = refcAsSuper.getSuperclass();
2622 m2 = new MemberName(refcAsSuper,
2623 method.getName(),
2624 method.getMethodType(),
2625 REF_invokeSpecial);
2626 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2627 } while (m2 == null && // no method is found yet
2628 refc != refcAsSuper); // search up to refc
2629 if (m2 == null) throw new InternalError(method.toString());
2630 method = m2;
2631 refc = refcAsSuper;
2632 // redo basic checks
2633 checkMethod(refKind, refc, method);
2634 }
2635
2636 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
2637 MethodHandle mh = dmh;
2638 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
2639 if ((doRestrict && refKind == REF_invokeSpecial) ||
2640 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2641 mh = restrictReceiver(method, dmh, lookupClass());
2642 }
2643 mh = maybeBindCaller(method, mh, boundCallerClass);
2644 mh = mh.setVarargs(method);
2645 return mh;
2646 }
2647 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2648 Class<?> boundCallerClass)
2649 throws IllegalAccessException {
2650 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2651 return mh;
2652 Class<?> hostClass = lookupClass;
2653 if (!hasPrivateAccess()) // caller must have private access
2654 hostClass = boundCallerClass; // boundCallerClass came from a security manager style stack walk
2655 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2656 // Note: caller will apply varargs after this step happens.
2657 return cbmh;
2658 }
2659 /** Check access and get the requested field. */
2660 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2661 final boolean checkSecurity = true;
2662 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2663 }
2664 /** Check access and get the requested field, eliding security manager checks. */
2665 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2666 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2667 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2668 }
2669 /** Common code for all fields; do not call directly except from immediately above. */
2670 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2671 boolean checkSecurity) throws IllegalAccessException {
2672 checkField(refKind, refc, field);
2673 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2674 if (checkSecurity)
2675 checkSecurityManager(refc, field);
2676 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2677 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2678 restrictProtectedReceiver(field));
2679 if (doRestrict)
2680 return restrictReceiver(field, dmh, lookupClass());
2681 return dmh;
2682 }
2683 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2684 Class<?> refc, MemberName getField, MemberName putField)
2685 throws IllegalAccessException {
2686 final boolean checkSecurity = true;
2687 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2688 }
2689 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2690 Class<?> refc, MemberName getField, MemberName putField)
2691 throws IllegalAccessException {
2692 final boolean checkSecurity = false;
2693 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2694 }
2695 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2696 Class<?> refc, MemberName getField, MemberName putField,
2697 boolean checkSecurity) throws IllegalAccessException {
2698 assert getField.isStatic() == putField.isStatic();
2699 assert getField.isGetter() && putField.isSetter();
2700 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2701 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2702
2703 checkField(getRefKind, refc, getField);
2704 if (checkSecurity)
2705 checkSecurityManager(refc, getField);
2706
2707 if (!putField.isFinal()) {
2708 // A VarHandle does not support updates to final fields, any
2709 // such VarHandle to a final field will be read-only and
2710 // therefore the following write-based accessibility checks are
2711 // only required for non-final fields
2712 checkField(putRefKind, refc, putField);
2713 if (checkSecurity)
2714 checkSecurityManager(refc, putField);
2715 }
2716
2717 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2718 restrictProtectedReceiver(getField));
2719 if (doRestrict) {
2720 assert !getField.isStatic();
2721 // receiver type of VarHandle is too wide; narrow to caller
2722 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2723 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2724 }
2725 refc = lookupClass();
2726 }
2727 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2728 }
2729 /** Check access and get the requested constructor. */
2730 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2731 final boolean checkSecurity = true;
2732 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2733 }
2734 /** Check access and get the requested constructor, eliding security manager checks. */
2735 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2736 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2737 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2738 }
2739 /** Common code for all constructors; do not call directly except from immediately above. */
2740 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2741 boolean checkSecurity) throws IllegalAccessException {
2742 assert(ctor.isConstructor());
2743 checkAccess(REF_newInvokeSpecial, refc, ctor);
2744 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2745 if (checkSecurity)
2746 checkSecurityManager(refc, ctor);
2747 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2748 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2749 }
2750
2751 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2752 */
2753 /*non-public*/
2754 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2755 if (!(type instanceof Class || type instanceof MethodType))
2756 throw new InternalError("unresolved MemberName");
2757 MemberName member = new MemberName(refKind, defc, name, type);
2758 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2759 if (mh != null) {
2760 checkSymbolicClass(defc);
2761 return mh;
2762 }
2763 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2764 // Treat MethodHandle.invoke and invokeExact specially.
2765 mh = findVirtualForMH(member.getName(), member.getMethodType());
2766 if (mh != null) {
2767 return mh;
2768 }
2769 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
2770 // Treat signature-polymorphic methods on VarHandle specially.
2771 mh = findVirtualForVH(member.getName(), member.getMethodType());
2772 if (mh != null) {
2773 return mh;
2774 }
2775 }
2776 MemberName resolved = resolveOrFail(refKind, member);
2777 mh = getDirectMethodForConstant(refKind, defc, resolved);
2778 if (mh instanceof DirectMethodHandle
2779 && canBeCached(refKind, defc, resolved)) {
2780 MemberName key = mh.internalMemberName();
2781 if (key != null) {
2782 key = key.asNormalOriginal();
2783 }
2784 if (member.equals(key)) { // better safe than sorry
2785 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2786 }
2787 }
2788 return mh;
2789 }
2790 private
2791 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2792 if (refKind == REF_invokeSpecial) {
2793 return false;
2794 }
2795 if (!Modifier.isPublic(defc.getModifiers()) ||
2796 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2797 !member.isPublic() ||
2798 member.isCallerSensitive()) {
2799 return false;
2800 }
2801 ClassLoader loader = defc.getClassLoader();
2802 if (loader != null) {
2803 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2804 boolean found = false;
2805 while (sysl != null) {
2806 if (loader == sysl) { found = true; break; }
2807 sysl = sysl.getParent();
2808 }
2809 if (!found) {
2810 return false;
2811 }
2812 }
2813 try {
2814 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
2815 new MemberName(refKind, defc, member.getName(), member.getType()));
2816 if (resolved2 == null) {
2817 return false;
2818 }
2819 checkSecurityManager(defc, resolved2);
2820 } catch (SecurityException ex) {
2821 return false;
2822 }
2823 return true;
2824 }
2825 private
2826 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2827 throws ReflectiveOperationException {
2828 if (MethodHandleNatives.refKindIsField(refKind)) {
2829 return getDirectFieldNoSecurityManager(refKind, defc, member);
2830 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2831 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2832 } else if (refKind == REF_newInvokeSpecial) {
2833 return getDirectConstructorNoSecurityManager(defc, member);
2834 }
2835 // oops
2836 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2837 }
2838
2839 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2840
2841 /**
2842 * Property of a class to be defined via the
2843 * {@link Lookup#defineClass(byte[], ClassProperty[]) Lookup.defineClass} method.
2844 *
2845 * @since 12
2846 * @see Lookup#defineClass(byte[], ClassProperty[])
2847 * @see Lookup#defineClassWithClassData(byte[], Object, ClassProperty[])
2848 */
2849 public enum ClassProperty {
2850 /**
2851 * A nestmate is a class that is in the same {@linkplain Class#getNestHost nest}
2852 * of a lookup class. It has access to the private members of all
2853 * classes and interfaces in the same nest.
2854 *
2855 * @see Class#getNestHost()
2856 */
2857 NESTMATE(NESTMATE_CLASS),
2858
2859 /**
2860 * A hidden class is a class that cannot be referenced by other
2861 * classes. A Java Virtual Machine implementation may hide
2862 * the hidden frames from {@linkplain Throwable#getStackTrace()
2863 * stack traces}.
2864 *
2865 * @see Class#isHidden()
2866 * @see StackWalker.Option#SHOW_HIDDEN_FRAMES
2867 */
2868 HIDDEN(NONFINDABLE_CLASS),
2869
2870 /**
2871 * A weak class is a class that may be unloaded even if
2872 * its defining class loader is
2873 * <a href="../ref/package.html#reachability">reachable</a>.
2874 * A weak class is {@linkplain #HIDDEN hidden}.
2875 *
2876 * @jls 12.7 Unloading of Classes and Interfaces
2877 */
2878 WEAK(WEAK_CLASS);
2879
2880 /* the flag value is used by VM at define class time */
2881 final int flag;
2882 ClassProperty(int flag) {
2883 this.flag = flag;
2884 }
2885 }
2886 }
2887
2888 /**
2889 * Produces a method handle constructing arrays of a desired type,
2890 * as if by the {@code anewarray} bytecode.
2891 * The return type of the method handle will be the array type.
2892 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2893 *
2894 * <p> If the returned method handle is invoked with a negative
2895 * array size, a {@code NegativeArraySizeException} will be thrown.
2896 *
2897 * @param arrayClass an array type
2898 * @return a method handle which can create arrays of the given type
2899 * @throws NullPointerException if the argument is {@code null}
2900 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2901 * @see java.lang.reflect.Array#newInstance(Class, int)
2902 * @jvms 6.5 {@code anewarray} Instruction
2903 * @since 9
2904 */
2905 public static
2906 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2907 if (!arrayClass.isArray()) {
2908 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2909 }
2910 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2911 bindTo(arrayClass.getComponentType());
2912 return ani.asType(ani.type().changeReturnType(arrayClass));
2913 }
2914
2915 /**
2916 * Produces a method handle returning the length of an array,
2917 * as if by the {@code arraylength} bytecode.
2918 * The type of the method handle will have {@code int} as return type,
2919 * and its sole argument will be the array type.
2920 *
2921 * <p> If the returned method handle is invoked with a {@code null}
2922 * array reference, a {@code NullPointerException} will be thrown.
2923 *
2924 * @param arrayClass an array type
2925 * @return a method handle which can retrieve the length of an array of the given array type
2926 * @throws NullPointerException if the argument is {@code null}
2927 * @throws IllegalArgumentException if arrayClass is not an array type
2928 * @jvms 6.5 {@code arraylength} Instruction
2929 * @since 9
2930 */
2931 public static
2932 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2933 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2934 }
2935
2936 /**
2937 * Produces a method handle giving read access to elements of an array,
2938 * as if by the {@code aaload} bytecode.
2939 * The type of the method handle will have a return type of the array's
2940 * element type. Its first argument will be the array type,
2941 * and the second will be {@code int}.
2942 *
2943 * <p> When the returned method handle is invoked,
2944 * the array reference and array index are checked.
2945 * A {@code NullPointerException} will be thrown if the array reference
2946 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2947 * thrown if the index is negative or if it is greater than or equal to
2948 * the length of the array.
2949 *
2950 * @param arrayClass an array type
2951 * @return a method handle which can load values from the given array type
2952 * @throws NullPointerException if the argument is null
2953 * @throws IllegalArgumentException if arrayClass is not an array type
2954 * @jvms 6.5 {@code aaload} Instruction
2955 */
2956 public static
2957 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2958 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2959 }
2960
2961 /**
2962 * Produces a method handle giving write access to elements of an array,
2963 * as if by the {@code astore} bytecode.
2964 * The type of the method handle will have a void return type.
2965 * Its last argument will be the array's element type.
2966 * The first and second arguments will be the array type and int.
2967 *
2968 * <p> When the returned method handle is invoked,
2969 * the array reference and array index are checked.
2970 * A {@code NullPointerException} will be thrown if the array reference
2971 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2972 * thrown if the index is negative or if it is greater than or equal to
2973 * the length of the array.
2974 *
2975 * @param arrayClass the class of an array
2976 * @return a method handle which can store values into the array type
2977 * @throws NullPointerException if the argument is null
2978 * @throws IllegalArgumentException if arrayClass is not an array type
2979 * @jvms 6.5 {@code aastore} Instruction
2980 */
2981 public static
2982 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2983 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2984 }
2985
2986 /**
2987 * Produces a VarHandle giving access to elements of an array of type
2988 * {@code arrayClass}. The VarHandle's variable type is the component type
2989 * of {@code arrayClass} and the list of coordinate types is
2990 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2991 * corresponds to an argument that is an index into an array.
2992 * <p>
2993 * Certain access modes of the returned VarHandle are unsupported under
2994 * the following conditions:
2995 * <ul>
2996 * <li>if the component type is anything other than {@code byte},
2997 * {@code short}, {@code char}, {@code int}, {@code long},
2998 * {@code float}, or {@code double} then numeric atomic update access
2999 * modes are unsupported.
3000 * <li>if the field type is anything other than {@code boolean},
3001 * {@code byte}, {@code short}, {@code char}, {@code int} or
3002 * {@code long} then bitwise atomic update access modes are
3003 * unsupported.
3004 * </ul>
3005 * <p>
3006 * If the component type is {@code float} or {@code double} then numeric
3007 * and atomic update access modes compare values using their bitwise
3008 * representation (see {@link Float#floatToRawIntBits} and
3009 * {@link Double#doubleToRawLongBits}, respectively).
3010 *
3011 * <p> When the returned {@code VarHandle} is invoked,
3012 * the array reference and array index are checked.
3013 * A {@code NullPointerException} will be thrown if the array reference
3014 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
3015 * thrown if the index is negative or if it is greater than or equal to
3016 * the length of the array.
3017 *
3018 * @apiNote
3019 * Bitwise comparison of {@code float} values or {@code double} values,
3020 * as performed by the numeric and atomic update access modes, differ
3021 * from the primitive {@code ==} operator and the {@link Float#equals}
3022 * and {@link Double#equals} methods, specifically with respect to
3023 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3024 * Care should be taken when performing a compare and set or a compare
3025 * and exchange operation with such values since the operation may
3026 * unexpectedly fail.
3027 * There are many possible NaN values that are considered to be
3028 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3029 * provided by Java can distinguish between them. Operation failure can
3030 * occur if the expected or witness value is a NaN value and it is
3031 * transformed (perhaps in a platform specific manner) into another NaN
3032 * value, and thus has a different bitwise representation (see
3033 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3034 * details).
3035 * The values {@code -0.0} and {@code +0.0} have different bitwise
3036 * representations but are considered equal when using the primitive
3037 * {@code ==} operator. Operation failure can occur if, for example, a
3038 * numeric algorithm computes an expected value to be say {@code -0.0}
3039 * and previously computed the witness value to be say {@code +0.0}.
3040 * @param arrayClass the class of an array, of type {@code T[]}
3041 * @return a VarHandle giving access to elements of an array
3042 * @throws NullPointerException if the arrayClass is null
3043 * @throws IllegalArgumentException if arrayClass is not an array type
3044 * @since 9
3045 */
3046 public static
3047 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
3048 return VarHandles.makeArrayElementHandle(arrayClass);
3049 }
3050
3051 /**
3052 * Produces a VarHandle giving access to elements of a {@code byte[]} array
3053 * viewed as if it were a different primitive array type, such as
3054 * {@code int[]} or {@code long[]}.
3055 * The VarHandle's variable type is the component type of
3056 * {@code viewArrayClass} and the list of coordinate types is
3057 * {@code (byte[], int)}, where the {@code int} coordinate type
3058 * corresponds to an argument that is an index into a {@code byte[]} array.
3059 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
3060 * array, composing bytes to or from a value of the component type of
3061 * {@code viewArrayClass} according to the given endianness.
3062 * <p>
3063 * The supported component types (variables types) are {@code short},
3064 * {@code char}, {@code int}, {@code long}, {@code float} and
3065 * {@code double}.
3066 * <p>
3067 * Access of bytes at a given index will result in an
3068 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3069 * or greater than the {@code byte[]} array length minus the size (in bytes)
3070 * of {@code T}.
3071 * <p>
3072 * Access of bytes at an index may be aligned or misaligned for {@code T},
3073 * with respect to the underlying memory address, {@code A} say, associated
3074 * with the array and index.
3075 * If access is misaligned then access for anything other than the
3076 * {@code get} and {@code set} access modes will result in an
3077 * {@code IllegalStateException}. In such cases atomic access is only
3078 * guaranteed with respect to the largest power of two that divides the GCD
3079 * of {@code A} and the size (in bytes) of {@code T}.
3080 * If access is aligned then following access modes are supported and are
3081 * guaranteed to support atomic access:
3082 * <ul>
3083 * <li>read write access modes for all {@code T}, with the exception of
3084 * access modes {@code get} and {@code set} for {@code long} and
3085 * {@code double} on 32-bit platforms.
3086 * <li>atomic update access modes for {@code int}, {@code long},
3087 * {@code float} or {@code double}.
3088 * (Future major platform releases of the JDK may support additional
3089 * types for certain currently unsupported access modes.)
3090 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3091 * (Future major platform releases of the JDK may support additional
3092 * numeric types for certain currently unsupported access modes.)
3093 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3094 * (Future major platform releases of the JDK may support additional
3095 * numeric types for certain currently unsupported access modes.)
3096 * </ul>
3097 * <p>
3098 * Misaligned access, and therefore atomicity guarantees, may be determined
3099 * for {@code byte[]} arrays without operating on a specific array. Given
3100 * an {@code index}, {@code T} and it's corresponding boxed type,
3101 * {@code T_BOX}, misalignment may be determined as follows:
3102 * <pre>{@code
3103 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3104 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
3105 * alignmentOffset(0, sizeOfT);
3106 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
3107 * boolean isMisaligned = misalignedAtIndex != 0;
3108 * }</pre>
3109 * <p>
3110 * If the variable type is {@code float} or {@code double} then atomic
3111 * update access modes compare values using their bitwise representation
3112 * (see {@link Float#floatToRawIntBits} and
3113 * {@link Double#doubleToRawLongBits}, respectively).
3114 * @param viewArrayClass the view array class, with a component type of
3115 * type {@code T}
3116 * @param byteOrder the endianness of the view array elements, as
3117 * stored in the underlying {@code byte} array
3118 * @return a VarHandle giving access to elements of a {@code byte[]} array
3119 * viewed as if elements corresponding to the components type of the view
3120 * array class
3121 * @throws NullPointerException if viewArrayClass or byteOrder is null
3122 * @throws IllegalArgumentException if viewArrayClass is not an array type
3123 * @throws UnsupportedOperationException if the component type of
3124 * viewArrayClass is not supported as a variable type
3125 * @since 9
3126 */
3127 public static
3128 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
3129 ByteOrder byteOrder) throws IllegalArgumentException {
3130 Objects.requireNonNull(byteOrder);
3131 return VarHandles.byteArrayViewHandle(viewArrayClass,
3132 byteOrder == ByteOrder.BIG_ENDIAN);
3133 }
3134
3135 /**
3136 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
3137 * viewed as if it were an array of elements of a different primitive
3138 * component type to that of {@code byte}, such as {@code int[]} or
3139 * {@code long[]}.
3140 * The VarHandle's variable type is the component type of
3141 * {@code viewArrayClass} and the list of coordinate types is
3142 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
3143 * corresponds to an argument that is an index into a {@code byte[]} array.
3144 * The returned VarHandle accesses bytes at an index in a
3145 * {@code ByteBuffer}, composing bytes to or from a value of the component
3146 * type of {@code viewArrayClass} according to the given endianness.
3147 * <p>
3148 * The supported component types (variables types) are {@code short},
3149 * {@code char}, {@code int}, {@code long}, {@code float} and
3150 * {@code double}.
3151 * <p>
3152 * Access will result in a {@code ReadOnlyBufferException} for anything
3153 * other than the read access modes if the {@code ByteBuffer} is read-only.
3154 * <p>
3155 * Access of bytes at a given index will result in an
3156 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
3157 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
3158 * {@code T}.
3159 * <p>
3160 * Access of bytes at an index may be aligned or misaligned for {@code T},
3161 * with respect to the underlying memory address, {@code A} say, associated
3162 * with the {@code ByteBuffer} and index.
3163 * If access is misaligned then access for anything other than the
3164 * {@code get} and {@code set} access modes will result in an
3165 * {@code IllegalStateException}. In such cases atomic access is only
3166 * guaranteed with respect to the largest power of two that divides the GCD
3167 * of {@code A} and the size (in bytes) of {@code T}.
3168 * If access is aligned then following access modes are supported and are
3169 * guaranteed to support atomic access:
3170 * <ul>
3171 * <li>read write access modes for all {@code T}, with the exception of
3172 * access modes {@code get} and {@code set} for {@code long} and
3173 * {@code double} on 32-bit platforms.
3174 * <li>atomic update access modes for {@code int}, {@code long},
3175 * {@code float} or {@code double}.
3176 * (Future major platform releases of the JDK may support additional
3177 * types for certain currently unsupported access modes.)
3178 * <li>numeric atomic update access modes for {@code int} and {@code long}.
3179 * (Future major platform releases of the JDK may support additional
3180 * numeric types for certain currently unsupported access modes.)
3181 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
3182 * (Future major platform releases of the JDK may support additional
3183 * numeric types for certain currently unsupported access modes.)
3184 * </ul>
3185 * <p>
3186 * Misaligned access, and therefore atomicity guarantees, may be determined
3187 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
3188 * {@code index}, {@code T} and it's corresponding boxed type,
3189 * {@code T_BOX}, as follows:
3190 * <pre>{@code
3191 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
3192 * ByteBuffer bb = ...
3193 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
3194 * boolean isMisaligned = misalignedAtIndex != 0;
3195 * }</pre>
3196 * <p>
3197 * If the variable type is {@code float} or {@code double} then atomic
3198 * update access modes compare values using their bitwise representation
3199 * (see {@link Float#floatToRawIntBits} and
3200 * {@link Double#doubleToRawLongBits}, respectively).
3201 * @param viewArrayClass the view array class, with a component type of
3202 * type {@code T}
3203 * @param byteOrder the endianness of the view array elements, as
3204 * stored in the underlying {@code ByteBuffer} (Note this overrides the
3205 * endianness of a {@code ByteBuffer})
3206 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
3207 * viewed as if elements corresponding to the components type of the view
3208 * array class
3209 * @throws NullPointerException if viewArrayClass or byteOrder is null
3210 * @throws IllegalArgumentException if viewArrayClass is not an array type
3211 * @throws UnsupportedOperationException if the component type of
3212 * viewArrayClass is not supported as a variable type
3213 * @since 9
3214 */
3215 public static
3216 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
3217 ByteOrder byteOrder) throws IllegalArgumentException {
3218 Objects.requireNonNull(byteOrder);
3219 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
3220 byteOrder == ByteOrder.BIG_ENDIAN);
3221 }
3222
3223
3224 /// method handle invocation (reflective style)
3225
3226 /**
3227 * Produces a method handle which will invoke any method handle of the
3228 * given {@code type}, with a given number of trailing arguments replaced by
3229 * a single trailing {@code Object[]} array.
3230 * The resulting invoker will be a method handle with the following
3231 * arguments:
3232 * <ul>
3233 * <li>a single {@code MethodHandle} target
3234 * <li>zero or more leading values (counted by {@code leadingArgCount})
3235 * <li>an {@code Object[]} array containing trailing arguments
3236 * </ul>
3237 * <p>
3238 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
3239 * the indicated {@code type}.
3240 * That is, if the target is exactly of the given {@code type}, it will behave
3241 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
3242 * is used to convert the target to the required {@code type}.
3243 * <p>
3244 * The type of the returned invoker will not be the given {@code type}, but rather
3245 * will have all parameters except the first {@code leadingArgCount}
3246 * replaced by a single array of type {@code Object[]}, which will be
3247 * the final parameter.
3248 * <p>
3249 * Before invoking its target, the invoker will spread the final array, apply
3250 * reference casts as necessary, and unbox and widen primitive arguments.
3251 * If, when the invoker is called, the supplied array argument does
3252 * not have the correct number of elements, the invoker will throw
3253 * an {@link IllegalArgumentException} instead of invoking the target.
3254 * <p>
3255 * This method is equivalent to the following code (though it may be more efficient):
3256 * <blockquote><pre>{@code
3257 MethodHandle invoker = MethodHandles.invoker(type);
3258 int spreadArgCount = type.parameterCount() - leadingArgCount;
3259 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
3260 return invoker;
3261 * }</pre></blockquote>
3262 * This method throws no reflective or security exceptions.
3263 * @param type the desired target type
3264 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
3265 * @return a method handle suitable for invoking any method handle of the given type
3266 * @throws NullPointerException if {@code type} is null
3267 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
3268 * the range from 0 to {@code type.parameterCount()} inclusive,
3269 * or if the resulting method handle's type would have
3270 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3271 */
3272 public static
3273 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
3274 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
3275 throw newIllegalArgumentException("bad argument count", leadingArgCount);
3276 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
3277 return type.invokers().spreadInvoker(leadingArgCount);
3278 }
3279
3280 /**
3281 * Produces a special <em>invoker method handle</em> which can be used to
3282 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
3283 * The resulting invoker will have a type which is
3284 * exactly equal to the desired type, except that it will accept
3285 * an additional leading argument of type {@code MethodHandle}.
3286 * <p>
3287 * This method is equivalent to the following code (though it may be more efficient):
3288 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
3289 *
3290 * <p style="font-size:smaller;">
3291 * <em>Discussion:</em>
3292 * Invoker method handles can be useful when working with variable method handles
3293 * of unknown types.
3294 * For example, to emulate an {@code invokeExact} call to a variable method
3295 * handle {@code M}, extract its type {@code T},
3296 * look up the invoker method {@code X} for {@code T},
3297 * and call the invoker method, as {@code X.invoke(T, A...)}.
3298 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
3299 * is unknown.)
3300 * If spreading, collecting, or other argument transformations are required,
3301 * they can be applied once to the invoker {@code X} and reused on many {@code M}
3302 * method handle values, as long as they are compatible with the type of {@code X}.
3303 * <p style="font-size:smaller;">
3304 * <em>(Note: The invoker method is not available via the Core Reflection API.
3305 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3306 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3307 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3308 * <p>
3309 * This method throws no reflective or security exceptions.
3310 * @param type the desired target type
3311 * @return a method handle suitable for invoking any method handle of the given type
3312 * @throws IllegalArgumentException if the resulting method handle's type would have
3313 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3314 */
3315 public static
3316 MethodHandle exactInvoker(MethodType type) {
3317 return type.invokers().exactInvoker();
3318 }
3319
3320 /**
3321 * Produces a special <em>invoker method handle</em> which can be used to
3322 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
3323 * The resulting invoker will have a type which is
3324 * exactly equal to the desired type, except that it will accept
3325 * an additional leading argument of type {@code MethodHandle}.
3326 * <p>
3327 * Before invoking its target, if the target differs from the expected type,
3328 * the invoker will apply reference casts as
3329 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
3330 * Similarly, the return value will be converted as necessary.
3331 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
3332 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
3333 * <p>
3334 * This method is equivalent to the following code (though it may be more efficient):
3335 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
3336 * <p style="font-size:smaller;">
3337 * <em>Discussion:</em>
3338 * A {@linkplain MethodType#genericMethodType general method type} is one which
3339 * mentions only {@code Object} arguments and return values.
3340 * An invoker for such a type is capable of calling any method handle
3341 * of the same arity as the general type.
3342 * <p style="font-size:smaller;">
3343 * <em>(Note: The invoker method is not available via the Core Reflection API.
3344 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
3345 * on the declared {@code invokeExact} or {@code invoke} method will raise an
3346 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
3347 * <p>
3348 * This method throws no reflective or security exceptions.
3349 * @param type the desired target type
3350 * @return a method handle suitable for invoking any method handle convertible to the given type
3351 * @throws IllegalArgumentException if the resulting method handle's type would have
3352 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3353 */
3354 public static
3355 MethodHandle invoker(MethodType type) {
3356 return type.invokers().genericInvoker();
3357 }
3358
3359 /**
3360 * Produces a special <em>invoker method handle</em> which can be used to
3361 * invoke a signature-polymorphic access mode method on any VarHandle whose
3362 * associated access mode type is compatible with the given type.
3363 * The resulting invoker will have a type which is exactly equal to the
3364 * desired given type, except that it will accept an additional leading
3365 * argument of type {@code VarHandle}.
3366 *
3367 * @param accessMode the VarHandle access mode
3368 * @param type the desired target type
3369 * @return a method handle suitable for invoking an access mode method of
3370 * any VarHandle whose access mode type is of the given type.
3371 * @since 9
3372 */
3373 static public
3374 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3375 return type.invokers().varHandleMethodExactInvoker(accessMode);
3376 }
3377
3378 /**
3379 * Produces a special <em>invoker method handle</em> which can be used to
3380 * invoke a signature-polymorphic access mode method on any VarHandle whose
3381 * associated access mode type is compatible with the given type.
3382 * The resulting invoker will have a type which is exactly equal to the
3383 * desired given type, except that it will accept an additional leading
3384 * argument of type {@code VarHandle}.
3385 * <p>
3386 * Before invoking its target, if the access mode type differs from the
3387 * desired given type, the invoker will apply reference casts as necessary
3388 * and box, unbox, or widen primitive values, as if by
3389 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3390 * converted as necessary.
3391 * <p>
3392 * This method is equivalent to the following code (though it may be more
3393 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3394 *
3395 * @param accessMode the VarHandle access mode
3396 * @param type the desired target type
3397 * @return a method handle suitable for invoking an access mode method of
3398 * any VarHandle whose access mode type is convertible to the given
3399 * type.
3400 * @since 9
3401 */
3402 static public
3403 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3404 return type.invokers().varHandleMethodInvoker(accessMode);
3405 }
3406
3407 static /*non-public*/
3408 MethodHandle basicInvoker(MethodType type) {
3409 return type.invokers().basicInvoker();
3410 }
3411
3412 /// method handle modification (creation from other method handles)
3413
3414 /**
3415 * Produces a method handle which adapts the type of the
3416 * given method handle to a new type by pairwise argument and return type conversion.
3417 * The original type and new type must have the same number of arguments.
3418 * The resulting method handle is guaranteed to report a type
3419 * which is equal to the desired new type.
3420 * <p>
3421 * If the original type and new type are equal, returns target.
3422 * <p>
3423 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3424 * and some additional conversions are also applied if those conversions fail.
3425 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3426 * if possible, before or instead of any conversions done by {@code asType}:
3427 * <ul>
3428 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3429 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3430 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3431 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3432 * the boolean is converted to a byte value, 1 for true, 0 for false.
3433 * (This treatment follows the usage of the bytecode verifier.)
3434 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3435 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3436 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3437 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3438 * then a Java casting conversion (JLS 5.5) is applied.
3439 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3440 * widening and/or narrowing.)
3441 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3442 * conversion will be applied at runtime, possibly followed
3443 * by a Java casting conversion (JLS 5.5) on the primitive value,
3444 * possibly followed by a conversion from byte to boolean by testing
3445 * the low-order bit.
3446 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3447 * and if the reference is null at runtime, a zero value is introduced.
3448 * </ul>
3449 * @param target the method handle to invoke after arguments are retyped
3450 * @param newType the expected type of the new method handle
3451 * @return a method handle which delegates to the target after performing
3452 * any necessary argument conversions, and arranges for any
3453 * necessary return value conversions
3454 * @throws NullPointerException if either argument is null
3455 * @throws WrongMethodTypeException if the conversion cannot be made
3456 * @see MethodHandle#asType
3457 */
3458 public static
3459 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3460 explicitCastArgumentsChecks(target, newType);
3461 // use the asTypeCache when possible:
3462 MethodType oldType = target.type();
3463 if (oldType == newType) return target;
3464 if (oldType.explicitCastEquivalentToAsType(newType)) {
3465 return target.asFixedArity().asType(newType);
3466 }
3467 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3468 }
3469
3470 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3471 if (target.type().parameterCount() != newType.parameterCount()) {
3472 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3473 }
3474 }
3475
3476 /**
3477 * Produces a method handle which adapts the calling sequence of the
3478 * given method handle to a new type, by reordering the arguments.
3479 * The resulting method handle is guaranteed to report a type
3480 * which is equal to the desired new type.
3481 * <p>
3482 * The given array controls the reordering.
3483 * Call {@code #I} the number of incoming parameters (the value
3484 * {@code newType.parameterCount()}, and call {@code #O} the number
3485 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3486 * Then the length of the reordering array must be {@code #O},
3487 * and each element must be a non-negative number less than {@code #I}.
3488 * For every {@code N} less than {@code #O}, the {@code N}-th
3489 * outgoing argument will be taken from the {@code I}-th incoming
3490 * argument, where {@code I} is {@code reorder[N]}.
3491 * <p>
3492 * No argument or return value conversions are applied.
3493 * The type of each incoming argument, as determined by {@code newType},
3494 * must be identical to the type of the corresponding outgoing parameter
3495 * or parameters in the target method handle.
3496 * The return type of {@code newType} must be identical to the return
3497 * type of the original target.
3498 * <p>
3499 * The reordering array need not specify an actual permutation.
3500 * An incoming argument will be duplicated if its index appears
3501 * more than once in the array, and an incoming argument will be dropped
3502 * if its index does not appear in the array.
3503 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3504 * incoming arguments which are not mentioned in the reordering array
3505 * may be of any type, as determined only by {@code newType}.
3506 * <blockquote><pre>{@code
3507 import static java.lang.invoke.MethodHandles.*;
3508 import static java.lang.invoke.MethodType.*;
3509 ...
3510 MethodType intfn1 = methodType(int.class, int.class);
3511 MethodType intfn2 = methodType(int.class, int.class, int.class);
3512 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3513 assert(sub.type().equals(intfn2));
3514 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3515 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3516 assert((int)rsub.invokeExact(1, 100) == 99);
3517 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3518 assert(add.type().equals(intfn2));
3519 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3520 assert(twice.type().equals(intfn1));
3521 assert((int)twice.invokeExact(21) == 42);
3522 * }</pre></blockquote>
3523 * <p>
3524 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3525 * variable-arity method handle}, even if the original target method handle was.
3526 * @param target the method handle to invoke after arguments are reordered
3527 * @param newType the expected type of the new method handle
3528 * @param reorder an index array which controls the reordering
3529 * @return a method handle which delegates to the target after it
3530 * drops unused arguments and moves and/or duplicates the other arguments
3531 * @throws NullPointerException if any argument is null
3532 * @throws IllegalArgumentException if the index array length is not equal to
3533 * the arity of the target, or if any index array element
3534 * not a valid index for a parameter of {@code newType},
3535 * or if two corresponding parameter types in
3536 * {@code target.type()} and {@code newType} are not identical,
3537 */
3538 public static
3539 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3540 reorder = reorder.clone(); // get a private copy
3541 MethodType oldType = target.type();
3542 permuteArgumentChecks(reorder, newType, oldType);
3543 // first detect dropped arguments and handle them separately
3544 int[] originalReorder = reorder;
3545 BoundMethodHandle result = target.rebind();
3546 LambdaForm form = result.form;
3547 int newArity = newType.parameterCount();
3548 // Normalize the reordering into a real permutation,
3549 // by removing duplicates and adding dropped elements.
3550 // This somewhat improves lambda form caching, as well
3551 // as simplifying the transform by breaking it up into steps.
3552 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3553 if (ddIdx > 0) {
3554 // We found a duplicated entry at reorder[ddIdx].
3555 // Example: (x,y,z)->asList(x,y,z)
3556 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3557 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3558 // The starred element corresponds to the argument
3559 // deleted by the dupArgumentForm transform.
3560 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3561 boolean killFirst = false;
3562 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3563 // Set killFirst if the dup is larger than an intervening position.
3564 // This will remove at least one inversion from the permutation.
3565 if (dupVal > val) killFirst = true;
3566 }
3567 if (!killFirst) {
3568 srcPos = dstPos;
3569 dstPos = ddIdx;
3570 }
3571 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3572 assert (reorder[srcPos] == reorder[dstPos]);
3573 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3574 // contract the reordering by removing the element at dstPos
3575 int tailPos = dstPos + 1;
3576 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3577 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3578 } else {
3579 int dropVal = ~ddIdx, insPos = 0;
3580 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3581 // Find first element of reorder larger than dropVal.
3582 // This is where we will insert the dropVal.
3583 insPos += 1;
3584 }
3585 Class<?> ptype = newType.parameterType(dropVal);
3586 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3587 oldType = oldType.insertParameterTypes(insPos, ptype);
3588 // expand the reordering by inserting an element at insPos
3589 int tailPos = insPos + 1;
3590 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3591 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3592 reorder[insPos] = dropVal;
3593 }
3594 assert (permuteArgumentChecks(reorder, newType, oldType));
3595 }
3596 assert (reorder.length == newArity); // a perfect permutation
3597 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3598 form = form.editor().permuteArgumentsForm(1, reorder);
3599 if (newType == result.type() && form == result.internalForm())
3600 return result;
3601 return result.copyWith(newType, form);
3602 }
3603
3604 /**
3605 * Return an indication of any duplicate or omission in reorder.
3606 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3607 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3608 * Otherwise, return zero.
3609 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3610 */
3611 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3612 final int BIT_LIMIT = 63; // max number of bits in bit mask
3613 if (newArity < BIT_LIMIT) {
3614 long mask = 0;
3615 for (int i = 0; i < reorder.length; i++) {
3616 int arg = reorder[i];
3617 if (arg >= newArity) {
3618 return reorder.length;
3619 }
3620 long bit = 1L << arg;
3621 if ((mask & bit) != 0) {
3622 return i; // >0 indicates a dup
3623 }
3624 mask |= bit;
3625 }
3626 if (mask == (1L << newArity) - 1) {
3627 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3628 return 0;
3629 }
3630 // find first zero
3631 long zeroBit = Long.lowestOneBit(~mask);
3632 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3633 assert(zeroPos <= newArity);
3634 if (zeroPos == newArity) {
3635 return 0;
3636 }
3637 return ~zeroPos;
3638 } else {
3639 // same algorithm, different bit set
3640 BitSet mask = new BitSet(newArity);
3641 for (int i = 0; i < reorder.length; i++) {
3642 int arg = reorder[i];
3643 if (arg >= newArity) {
3644 return reorder.length;
3645 }
3646 if (mask.get(arg)) {
3647 return i; // >0 indicates a dup
3648 }
3649 mask.set(arg);
3650 }
3651 int zeroPos = mask.nextClearBit(0);
3652 assert(zeroPos <= newArity);
3653 if (zeroPos == newArity) {
3654 return 0;
3655 }
3656 return ~zeroPos;
3657 }
3658 }
3659
3660 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3661 if (newType.returnType() != oldType.returnType())
3662 throw newIllegalArgumentException("return types do not match",
3663 oldType, newType);
3664 if (reorder.length == oldType.parameterCount()) {
3665 int limit = newType.parameterCount();
3666 boolean bad = false;
3667 for (int j = 0; j < reorder.length; j++) {
3668 int i = reorder[j];
3669 if (i < 0 || i >= limit) {
3670 bad = true; break;
3671 }
3672 Class<?> src = newType.parameterType(i);
3673 Class<?> dst = oldType.parameterType(j);
3674 if (src != dst)
3675 throw newIllegalArgumentException("parameter types do not match after reorder",
3676 oldType, newType);
3677 }
3678 if (!bad) return true;
3679 }
3680 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3681 }
3682
3683 /**
3684 * Produces a method handle of the requested return type which returns the given
3685 * constant value every time it is invoked.
3686 * <p>
3687 * Before the method handle is returned, the passed-in value is converted to the requested type.
3688 * If the requested type is primitive, widening primitive conversions are attempted,
3689 * else reference conversions are attempted.
3690 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3691 * @param type the return type of the desired method handle
3692 * @param value the value to return
3693 * @return a method handle of the given return type and no arguments, which always returns the given value
3694 * @throws NullPointerException if the {@code type} argument is null
3695 * @throws ClassCastException if the value cannot be converted to the required return type
3696 * @throws IllegalArgumentException if the given type is {@code void.class}
3697 */
3698 public static
3699 MethodHandle constant(Class<?> type, Object value) {
3700 if (type.isPrimitive()) {
3701 if (type == void.class)
3702 throw newIllegalArgumentException("void type");
3703 Wrapper w = Wrapper.forPrimitiveType(type);
3704 value = w.convert(value, type);
3705 if (w.zero().equals(value))
3706 return zero(w, type);
3707 return insertArguments(identity(type), 0, value);
3708 } else {
3709 if (value == null)
3710 return zero(Wrapper.OBJECT, type);
3711 return identity(type).bindTo(value);
3712 }
3713 }
3714
3715 /**
3716 * Produces a method handle which returns its sole argument when invoked.
3717 * @param type the type of the sole parameter and return value of the desired method handle
3718 * @return a unary method handle which accepts and returns the given type
3719 * @throws NullPointerException if the argument is null
3720 * @throws IllegalArgumentException if the given type is {@code void.class}
3721 */
3722 public static
3723 MethodHandle identity(Class<?> type) {
3724 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3725 int pos = btw.ordinal();
3726 MethodHandle ident = IDENTITY_MHS[pos];
3727 if (ident == null) {
3728 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3729 }
3730 if (ident.type().returnType() == type)
3731 return ident;
3732 // something like identity(Foo.class); do not bother to intern these
3733 assert (btw == Wrapper.OBJECT);
3734 return makeIdentity(type);
3735 }
3736
3737 /**
3738 * Produces a constant method handle of the requested return type which
3739 * returns the default value for that type every time it is invoked.
3740 * The resulting constant method handle will have no side effects.
3741 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3742 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3743 * since {@code explicitCastArguments} converts {@code null} to default values.
3744 * @param type the expected return type of the desired method handle
3745 * @return a constant method handle that takes no arguments
3746 * and returns the default value of the given type (or void, if the type is void)
3747 * @throws NullPointerException if the argument is null
3748 * @see MethodHandles#constant
3749 * @see MethodHandles#empty
3750 * @see MethodHandles#explicitCastArguments
3751 * @since 9
3752 */
3753 public static MethodHandle zero(Class<?> type) {
3754 Objects.requireNonNull(type);
3755 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3756 }
3757
3758 private static MethodHandle identityOrVoid(Class<?> type) {
3759 return type == void.class ? zero(type) : identity(type);
3760 }
3761
3762 /**
3763 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3764 * and returns a suitable default depending on the return type.
3765 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3766 * <p>The returned method handle is equivalent to
3767 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3768 *
3769 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3770 * {@code guardWithTest(pred, target, empty(target.type())}.
3771 * @param type the type of the desired method handle
3772 * @return a constant method handle of the given type, which returns a default value of the given return type
3773 * @throws NullPointerException if the argument is null
3774 * @see MethodHandles#zero
3775 * @see MethodHandles#constant
3776 * @since 9
3777 */
3778 public static MethodHandle empty(MethodType type) {
3779 Objects.requireNonNull(type);
3780 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3781 }
3782
3783 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3784 private static MethodHandle makeIdentity(Class<?> ptype) {
3785 MethodType mtype = methodType(ptype, ptype);
3786 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3787 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3788 }
3789
3790 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3791 int pos = btw.ordinal();
3792 MethodHandle zero = ZERO_MHS[pos];
3793 if (zero == null) {
3794 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3795 }
3796 if (zero.type().returnType() == rtype)
3797 return zero;
3798 assert(btw == Wrapper.OBJECT);
3799 return makeZero(rtype);
3800 }
3801 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3802 private static MethodHandle makeZero(Class<?> rtype) {
3803 MethodType mtype = methodType(rtype);
3804 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3805 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3806 }
3807
3808 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3809 // Simulate a CAS, to avoid racy duplication of results.
3810 MethodHandle prev = cache[pos];
3811 if (prev != null) return prev;
3812 return cache[pos] = value;
3813 }
3814
3815 /**
3816 * Provides a target method handle with one or more <em>bound arguments</em>
3817 * in advance of the method handle's invocation.
3818 * The formal parameters to the target corresponding to the bound
3819 * arguments are called <em>bound parameters</em>.
3820 * Returns a new method handle which saves away the bound arguments.
3821 * When it is invoked, it receives arguments for any non-bound parameters,
3822 * binds the saved arguments to their corresponding parameters,
3823 * and calls the original target.
3824 * <p>
3825 * The type of the new method handle will drop the types for the bound
3826 * parameters from the original target type, since the new method handle
3827 * will no longer require those arguments to be supplied by its callers.
3828 * <p>
3829 * Each given argument object must match the corresponding bound parameter type.
3830 * If a bound parameter type is a primitive, the argument object
3831 * must be a wrapper, and will be unboxed to produce the primitive value.
3832 * <p>
3833 * The {@code pos} argument selects which parameters are to be bound.
3834 * It may range between zero and <i>N-L</i> (inclusively),
3835 * where <i>N</i> is the arity of the target method handle
3836 * and <i>L</i> is the length of the values array.
3837 * <p>
3838 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3839 * variable-arity method handle}, even if the original target method handle was.
3840 * @param target the method handle to invoke after the argument is inserted
3841 * @param pos where to insert the argument (zero for the first)
3842 * @param values the series of arguments to insert
3843 * @return a method handle which inserts an additional argument,
3844 * before calling the original method handle
3845 * @throws NullPointerException if the target or the {@code values} array is null
3846 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
3847 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
3848 * is the length of the values array.
3849 * @throws ClassCastException if an argument does not match the corresponding bound parameter
3850 * type.
3851 * @see MethodHandle#bindTo
3852 */
3853 public static
3854 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3855 int insCount = values.length;
3856 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3857 if (insCount == 0) return target;
3858 BoundMethodHandle result = target.rebind();
3859 for (int i = 0; i < insCount; i++) {
3860 Object value = values[i];
3861 Class<?> ptype = ptypes[pos+i];
3862 if (ptype.isPrimitive()) {
3863 result = insertArgumentPrimitive(result, pos, ptype, value);
3864 } else {
3865 value = ptype.cast(value); // throw CCE if needed
3866 result = result.bindArgumentL(pos, value);
3867 }
3868 }
3869 return result;
3870 }
3871
3872 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3873 Class<?> ptype, Object value) {
3874 Wrapper w = Wrapper.forPrimitiveType(ptype);
3875 // perform unboxing and/or primitive conversion
3876 value = w.convert(value, ptype);
3877 switch (w) {
3878 case INT: return result.bindArgumentI(pos, (int)value);
3879 case LONG: return result.bindArgumentJ(pos, (long)value);
3880 case FLOAT: return result.bindArgumentF(pos, (float)value);
3881 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3882 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3883 }
3884 }
3885
3886 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3887 MethodType oldType = target.type();
3888 int outargs = oldType.parameterCount();
3889 int inargs = outargs - insCount;
3890 if (inargs < 0)
3891 throw newIllegalArgumentException("too many values to insert");
3892 if (pos < 0 || pos > inargs)
3893 throw newIllegalArgumentException("no argument type to append");
3894 return oldType.ptypes();
3895 }
3896
3897 /**
3898 * Produces a method handle which will discard some dummy arguments
3899 * before calling some other specified <i>target</i> method handle.
3900 * The type of the new method handle will be the same as the target's type,
3901 * except it will also include the dummy argument types,
3902 * at some given position.
3903 * <p>
3904 * The {@code pos} argument may range between zero and <i>N</i>,
3905 * where <i>N</i> is the arity of the target.
3906 * If {@code pos} is zero, the dummy arguments will precede
3907 * the target's real arguments; if {@code pos} is <i>N</i>
3908 * they will come after.
3909 * <p>
3910 * <b>Example:</b>
3911 * <blockquote><pre>{@code
3912 import static java.lang.invoke.MethodHandles.*;
3913 import static java.lang.invoke.MethodType.*;
3914 ...
3915 MethodHandle cat = lookup().findVirtual(String.class,
3916 "concat", methodType(String.class, String.class));
3917 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3918 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3919 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3920 assertEquals(bigType, d0.type());
3921 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3922 * }</pre></blockquote>
3923 * <p>
3924 * This method is also equivalent to the following code:
3925 * <blockquote><pre>
3926 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3927 * </pre></blockquote>
3928 * @param target the method handle to invoke after the arguments are dropped
3929 * @param valueTypes the type(s) of the argument(s) to drop
3930 * @param pos position of first argument to drop (zero for the leftmost)
3931 * @return a method handle which drops arguments of the given types,
3932 * before calling the original method handle
3933 * @throws NullPointerException if the target is null,
3934 * or if the {@code valueTypes} list or any of its elements is null
3935 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3936 * or if {@code pos} is negative or greater than the arity of the target,
3937 * or if the new method handle's type would have too many parameters
3938 */
3939 public static
3940 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3941 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3942 }
3943
3944 private static List<Class<?>> copyTypes(Object[] array) {
3945 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3946 }
3947
3948 private static
3949 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3950 MethodType oldType = target.type(); // get NPE
3951 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3952 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3953 if (dropped == 0) return target;
3954 BoundMethodHandle result = target.rebind();
3955 LambdaForm lform = result.form;
3956 int insertFormArg = 1 + pos;
3957 for (Class<?> ptype : valueTypes) {
3958 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3959 }
3960 result = result.copyWith(newType, lform);
3961 return result;
3962 }
3963
3964 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3965 int dropped = valueTypes.size();
3966 MethodType.checkSlotCount(dropped);
3967 int outargs = oldType.parameterCount();
3968 int inargs = outargs + dropped;
3969 if (pos < 0 || pos > outargs)
3970 throw newIllegalArgumentException("no argument type to remove"
3971 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3972 );
3973 return dropped;
3974 }
3975
3976 /**
3977 * Produces a method handle which will discard some dummy arguments
3978 * before calling some other specified <i>target</i> method handle.
3979 * The type of the new method handle will be the same as the target's type,
3980 * except it will also include the dummy argument types,
3981 * at some given position.
3982 * <p>
3983 * The {@code pos} argument may range between zero and <i>N</i>,
3984 * where <i>N</i> is the arity of the target.
3985 * If {@code pos} is zero, the dummy arguments will precede
3986 * the target's real arguments; if {@code pos} is <i>N</i>
3987 * they will come after.
3988 * @apiNote
3989 * <blockquote><pre>{@code
3990 import static java.lang.invoke.MethodHandles.*;
3991 import static java.lang.invoke.MethodType.*;
3992 ...
3993 MethodHandle cat = lookup().findVirtual(String.class,
3994 "concat", methodType(String.class, String.class));
3995 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3996 MethodHandle d0 = dropArguments(cat, 0, String.class);
3997 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3998 MethodHandle d1 = dropArguments(cat, 1, String.class);
3999 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
4000 MethodHandle d2 = dropArguments(cat, 2, String.class);
4001 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
4002 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
4003 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
4004 * }</pre></blockquote>
4005 * <p>
4006 * This method is also equivalent to the following code:
4007 * <blockquote><pre>
4008 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
4009 * </pre></blockquote>
4010 * @param target the method handle to invoke after the arguments are dropped
4011 * @param valueTypes the type(s) of the argument(s) to drop
4012 * @param pos position of first argument to drop (zero for the leftmost)
4013 * @return a method handle which drops arguments of the given types,
4014 * before calling the original method handle
4015 * @throws NullPointerException if the target is null,
4016 * or if the {@code valueTypes} array or any of its elements is null
4017 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
4018 * or if {@code pos} is negative or greater than the arity of the target,
4019 * or if the new method handle's type would have
4020 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4021 */
4022 public static
4023 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
4024 return dropArguments0(target, pos, copyTypes(valueTypes));
4025 }
4026
4027 // private version which allows caller some freedom with error handling
4028 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
4029 boolean nullOnFailure) {
4030 newTypes = copyTypes(newTypes.toArray());
4031 List<Class<?>> oldTypes = target.type().parameterList();
4032 int match = oldTypes.size();
4033 if (skip != 0) {
4034 if (skip < 0 || skip > match) {
4035 throw newIllegalArgumentException("illegal skip", skip, target);
4036 }
4037 oldTypes = oldTypes.subList(skip, match);
4038 match -= skip;
4039 }
4040 List<Class<?>> addTypes = newTypes;
4041 int add = addTypes.size();
4042 if (pos != 0) {
4043 if (pos < 0 || pos > add) {
4044 throw newIllegalArgumentException("illegal pos", pos, newTypes);
4045 }
4046 addTypes = addTypes.subList(pos, add);
4047 add -= pos;
4048 assert(addTypes.size() == add);
4049 }
4050 // Do not add types which already match the existing arguments.
4051 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
4052 if (nullOnFailure) {
4053 return null;
4054 }
4055 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
4056 }
4057 addTypes = addTypes.subList(match, add);
4058 add -= match;
4059 assert(addTypes.size() == add);
4060 // newTypes: ( P*[pos], M*[match], A*[add] )
4061 // target: ( S*[skip], M*[match] )
4062 MethodHandle adapter = target;
4063 if (add > 0) {
4064 adapter = dropArguments0(adapter, skip+ match, addTypes);
4065 }
4066 // adapter: (S*[skip], M*[match], A*[add] )
4067 if (pos > 0) {
4068 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
4069 }
4070 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
4071 return adapter;
4072 }
4073
4074 /**
4075 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
4076 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
4077 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
4078 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
4079 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
4080 * {@link #dropArguments(MethodHandle, int, Class[])}.
4081 * <p>
4082 * The resulting handle will have the same return type as the target handle.
4083 * <p>
4084 * In more formal terms, assume these two type lists:<ul>
4085 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
4086 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
4087 * {@code newTypes}.
4088 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
4089 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
4090 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
4091 * sub-list.
4092 * </ul>
4093 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
4094 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
4095 * {@link #dropArguments(MethodHandle, int, Class[])}.
4096 *
4097 * @apiNote
4098 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
4099 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
4100 * <blockquote><pre>{@code
4101 import static java.lang.invoke.MethodHandles.*;
4102 import static java.lang.invoke.MethodType.*;
4103 ...
4104 ...
4105 MethodHandle h0 = constant(boolean.class, true);
4106 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
4107 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
4108 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
4109 if (h1.type().parameterCount() < h2.type().parameterCount())
4110 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
4111 else
4112 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
4113 MethodHandle h3 = guardWithTest(h0, h1, h2);
4114 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
4115 * }</pre></blockquote>
4116 * @param target the method handle to adapt
4117 * @param skip number of targets parameters to disregard (they will be unchanged)
4118 * @param newTypes the list of types to match {@code target}'s parameter type list to
4119 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
4120 * @return a possibly adapted method handle
4121 * @throws NullPointerException if either argument is null
4122 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
4123 * or if {@code skip} is negative or greater than the arity of the target,
4124 * or if {@code pos} is negative or greater than the newTypes list size,
4125 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
4126 * {@code pos}.
4127 * @since 9
4128 */
4129 public static
4130 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
4131 Objects.requireNonNull(target);
4132 Objects.requireNonNull(newTypes);
4133 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
4134 }
4135
4136 /**
4137 * Adapts a target method handle by pre-processing
4138 * one or more of its arguments, each with its own unary filter function,
4139 * and then calling the target with each pre-processed argument
4140 * replaced by the result of its corresponding filter function.
4141 * <p>
4142 * The pre-processing is performed by one or more method handles,
4143 * specified in the elements of the {@code filters} array.
4144 * The first element of the filter array corresponds to the {@code pos}
4145 * argument of the target, and so on in sequence.
4146 * The filter functions are invoked in left to right order.
4147 * <p>
4148 * Null arguments in the array are treated as identity functions,
4149 * and the corresponding arguments left unchanged.
4150 * (If there are no non-null elements in the array, the original target is returned.)
4151 * Each filter is applied to the corresponding argument of the adapter.
4152 * <p>
4153 * If a filter {@code F} applies to the {@code N}th argument of
4154 * the target, then {@code F} must be a method handle which
4155 * takes exactly one argument. The type of {@code F}'s sole argument
4156 * replaces the corresponding argument type of the target
4157 * in the resulting adapted method handle.
4158 * The return type of {@code F} must be identical to the corresponding
4159 * parameter type of the target.
4160 * <p>
4161 * It is an error if there are elements of {@code filters}
4162 * (null or not)
4163 * which do not correspond to argument positions in the target.
4164 * <p><b>Example:</b>
4165 * <blockquote><pre>{@code
4166 import static java.lang.invoke.MethodHandles.*;
4167 import static java.lang.invoke.MethodType.*;
4168 ...
4169 MethodHandle cat = lookup().findVirtual(String.class,
4170 "concat", methodType(String.class, String.class));
4171 MethodHandle upcase = lookup().findVirtual(String.class,
4172 "toUpperCase", methodType(String.class));
4173 assertEquals("xy", (String) cat.invokeExact("x", "y"));
4174 MethodHandle f0 = filterArguments(cat, 0, upcase);
4175 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
4176 MethodHandle f1 = filterArguments(cat, 1, upcase);
4177 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
4178 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
4179 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
4180 * }</pre></blockquote>
4181 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4182 * denotes the return type of both the {@code target} and resulting adapter.
4183 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
4184 * of the parameters and arguments that precede and follow the filter position
4185 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
4186 * values of the filtered parameters and arguments; they also represent the
4187 * return types of the {@code filter[i]} handles. The latter accept arguments
4188 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
4189 * the resulting adapter.
4190 * <blockquote><pre>{@code
4191 * T target(P... p, A[i]... a[i], B... b);
4192 * A[i] filter[i](V[i]);
4193 * T adapter(P... p, V[i]... v[i], B... b) {
4194 * return target(p..., filter[i](v[i])..., b...);
4195 * }
4196 * }</pre></blockquote>
4197 * <p>
4198 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4199 * variable-arity method handle}, even if the original target method handle was.
4200 *
4201 * @param target the method handle to invoke after arguments are filtered
4202 * @param pos the position of the first argument to filter
4203 * @param filters method handles to call initially on filtered arguments
4204 * @return method handle which incorporates the specified argument filtering logic
4205 * @throws NullPointerException if the target is null
4206 * or if the {@code filters} array is null
4207 * @throws IllegalArgumentException if a non-null element of {@code filters}
4208 * does not match a corresponding argument type of target as described above,
4209 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
4210 * or if the resulting method handle's type would have
4211 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4212 */
4213 public static
4214 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
4215 filterArgumentsCheckArity(target, pos, filters);
4216 MethodHandle adapter = target;
4217 // process filters in reverse order so that the invocation of
4218 // the resulting adapter will invoke the filters in left-to-right order
4219 for (int i = filters.length - 1; i >= 0; --i) {
4220 MethodHandle filter = filters[i];
4221 if (filter == null) continue; // ignore null elements of filters
4222 adapter = filterArgument(adapter, pos + i, filter);
4223 }
4224 return adapter;
4225 }
4226
4227 /*non-public*/ static
4228 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
4229 filterArgumentChecks(target, pos, filter);
4230 MethodType targetType = target.type();
4231 MethodType filterType = filter.type();
4232 BoundMethodHandle result = target.rebind();
4233 Class<?> newParamType = filterType.parameterType(0);
4234 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
4235 MethodType newType = targetType.changeParameterType(pos, newParamType);
4236 result = result.copyWithExtendL(newType, lform, filter);
4237 return result;
4238 }
4239
4240 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
4241 MethodType targetType = target.type();
4242 int maxPos = targetType.parameterCount();
4243 if (pos + filters.length > maxPos)
4244 throw newIllegalArgumentException("too many filters");
4245 }
4246
4247 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4248 MethodType targetType = target.type();
4249 MethodType filterType = filter.type();
4250 if (filterType.parameterCount() != 1
4251 || filterType.returnType() != targetType.parameterType(pos))
4252 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4253 }
4254
4255 /**
4256 * Adapts a target method handle by pre-processing
4257 * a sub-sequence of its arguments with a filter (another method handle).
4258 * The pre-processed arguments are replaced by the result (if any) of the
4259 * filter function.
4260 * The target is then called on the modified (usually shortened) argument list.
4261 * <p>
4262 * If the filter returns a value, the target must accept that value as
4263 * its argument in position {@code pos}, preceded and/or followed by
4264 * any arguments not passed to the filter.
4265 * If the filter returns void, the target must accept all arguments
4266 * not passed to the filter.
4267 * No arguments are reordered, and a result returned from the filter
4268 * replaces (in order) the whole subsequence of arguments originally
4269 * passed to the adapter.
4270 * <p>
4271 * The argument types (if any) of the filter
4272 * replace zero or one argument types of the target, at position {@code pos},
4273 * in the resulting adapted method handle.
4274 * The return type of the filter (if any) must be identical to the
4275 * argument type of the target at position {@code pos}, and that target argument
4276 * is supplied by the return value of the filter.
4277 * <p>
4278 * In all cases, {@code pos} must be greater than or equal to zero, and
4279 * {@code pos} must also be less than or equal to the target's arity.
4280 * <p><b>Example:</b>
4281 * <blockquote><pre>{@code
4282 import static java.lang.invoke.MethodHandles.*;
4283 import static java.lang.invoke.MethodType.*;
4284 ...
4285 MethodHandle deepToString = publicLookup()
4286 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
4287
4288 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
4289 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
4290
4291 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
4292 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
4293
4294 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
4295 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
4296 assertEquals("[top, [up, down], strange]",
4297 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
4298
4299 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
4300 assertEquals("[top, [up, down], [strange]]",
4301 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
4302
4303 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
4304 assertEquals("[top, [[up, down, strange], charm], bottom]",
4305 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
4306 * }</pre></blockquote>
4307 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4308 * represents the return type of the {@code target} and resulting adapter.
4309 * {@code V}/{@code v} stand for the return type and value of the
4310 * {@code filter}, which are also found in the signature and arguments of
4311 * the {@code target}, respectively, unless {@code V} is {@code void}.
4312 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
4313 * and values preceding and following the collection position, {@code pos},
4314 * in the {@code target}'s signature. They also turn up in the resulting
4315 * adapter's signature and arguments, where they surround
4316 * {@code B}/{@code b}, which represent the parameter types and arguments
4317 * to the {@code filter} (if any).
4318 * <blockquote><pre>{@code
4319 * T target(A...,V,C...);
4320 * V filter(B...);
4321 * T adapter(A... a,B... b,C... c) {
4322 * V v = filter(b...);
4323 * return target(a...,v,c...);
4324 * }
4325 * // and if the filter has no arguments:
4326 * T target2(A...,V,C...);
4327 * V filter2();
4328 * T adapter2(A... a,C... c) {
4329 * V v = filter2();
4330 * return target2(a...,v,c...);
4331 * }
4332 * // and if the filter has a void return:
4333 * T target3(A...,C...);
4334 * void filter3(B...);
4335 * T adapter3(A... a,B... b,C... c) {
4336 * filter3(b...);
4337 * return target3(a...,c...);
4338 * }
4339 * }</pre></blockquote>
4340 * <p>
4341 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
4342 * one which first "folds" the affected arguments, and then drops them, in separate
4343 * steps as follows:
4344 * <blockquote><pre>{@code
4345 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
4346 * mh = MethodHandles.foldArguments(mh, coll); //step 1
4347 * }</pre></blockquote>
4348 * If the target method handle consumes no arguments besides than the result
4349 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
4350 * is equivalent to {@code filterReturnValue(coll, mh)}.
4351 * If the filter method handle {@code coll} consumes one argument and produces
4352 * a non-void result, then {@code collectArguments(mh, N, coll)}
4353 * is equivalent to {@code filterArguments(mh, N, coll)}.
4354 * Other equivalences are possible but would require argument permutation.
4355 * <p>
4356 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4357 * variable-arity method handle}, even if the original target method handle was.
4358 *
4359 * @param target the method handle to invoke after filtering the subsequence of arguments
4360 * @param pos the position of the first adapter argument to pass to the filter,
4361 * and/or the target argument which receives the result of the filter
4362 * @param filter method handle to call on the subsequence of arguments
4363 * @return method handle which incorporates the specified argument subsequence filtering logic
4364 * @throws NullPointerException if either argument is null
4365 * @throws IllegalArgumentException if the return type of {@code filter}
4366 * is non-void and is not the same as the {@code pos} argument of the target,
4367 * or if {@code pos} is not between 0 and the target's arity, inclusive,
4368 * or if the resulting method handle's type would have
4369 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4370 * @see MethodHandles#foldArguments
4371 * @see MethodHandles#filterArguments
4372 * @see MethodHandles#filterReturnValue
4373 */
4374 public static
4375 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4376 MethodType newType = collectArgumentsChecks(target, pos, filter);
4377 MethodType collectorType = filter.type();
4378 BoundMethodHandle result = target.rebind();
4379 LambdaForm lform;
4380 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4381 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4382 if (lform != null) {
4383 return result.copyWith(newType, lform);
4384 }
4385 }
4386 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4387 return result.copyWithExtendL(newType, lform, filter);
4388 }
4389
4390 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4391 MethodType targetType = target.type();
4392 MethodType filterType = filter.type();
4393 Class<?> rtype = filterType.returnType();
4394 List<Class<?>> filterArgs = filterType.parameterList();
4395 if (rtype == void.class) {
4396 return targetType.insertParameterTypes(pos, filterArgs);
4397 }
4398 if (rtype != targetType.parameterType(pos)) {
4399 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4400 }
4401 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4402 }
4403
4404 /**
4405 * Adapts a target method handle by post-processing
4406 * its return value (if any) with a filter (another method handle).
4407 * The result of the filter is returned from the adapter.
4408 * <p>
4409 * If the target returns a value, the filter must accept that value as
4410 * its only argument.
4411 * If the target returns void, the filter must accept no arguments.
4412 * <p>
4413 * The return type of the filter
4414 * replaces the return type of the target
4415 * in the resulting adapted method handle.
4416 * The argument type of the filter (if any) must be identical to the
4417 * return type of the target.
4418 * <p><b>Example:</b>
4419 * <blockquote><pre>{@code
4420 import static java.lang.invoke.MethodHandles.*;
4421 import static java.lang.invoke.MethodType.*;
4422 ...
4423 MethodHandle cat = lookup().findVirtual(String.class,
4424 "concat", methodType(String.class, String.class));
4425 MethodHandle length = lookup().findVirtual(String.class,
4426 "length", methodType(int.class));
4427 System.out.println((String) cat.invokeExact("x", "y")); // xy
4428 MethodHandle f0 = filterReturnValue(cat, length);
4429 System.out.println((int) f0.invokeExact("x", "y")); // 2
4430 * }</pre></blockquote>
4431 * <p>Here is pseudocode for the resulting adapter. In the code,
4432 * {@code T}/{@code t} represent the result type and value of the
4433 * {@code target}; {@code V}, the result type of the {@code filter}; and
4434 * {@code A}/{@code a}, the types and values of the parameters and arguments
4435 * of the {@code target} as well as the resulting adapter.
4436 * <blockquote><pre>{@code
4437 * T target(A...);
4438 * V filter(T);
4439 * V adapter(A... a) {
4440 * T t = target(a...);
4441 * return filter(t);
4442 * }
4443 * // and if the target has a void return:
4444 * void target2(A...);
4445 * V filter2();
4446 * V adapter2(A... a) {
4447 * target2(a...);
4448 * return filter2();
4449 * }
4450 * // and if the filter has a void return:
4451 * T target3(A...);
4452 * void filter3(V);
4453 * void adapter3(A... a) {
4454 * T t = target3(a...);
4455 * filter3(t);
4456 * }
4457 * }</pre></blockquote>
4458 * <p>
4459 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4460 * variable-arity method handle}, even if the original target method handle was.
4461 * @param target the method handle to invoke before filtering the return value
4462 * @param filter method handle to call on the return value
4463 * @return method handle which incorporates the specified return value filtering logic
4464 * @throws NullPointerException if either argument is null
4465 * @throws IllegalArgumentException if the argument list of {@code filter}
4466 * does not match the return type of target as described above
4467 */
4468 public static
4469 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4470 MethodType targetType = target.type();
4471 MethodType filterType = filter.type();
4472 filterReturnValueChecks(targetType, filterType);
4473 BoundMethodHandle result = target.rebind();
4474 BasicType rtype = BasicType.basicType(filterType.returnType());
4475 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4476 MethodType newType = targetType.changeReturnType(filterType.returnType());
4477 result = result.copyWithExtendL(newType, lform, filter);
4478 return result;
4479 }
4480
4481 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4482 Class<?> rtype = targetType.returnType();
4483 int filterValues = filterType.parameterCount();
4484 if (filterValues == 0
4485 ? (rtype != void.class)
4486 : (rtype != filterType.parameterType(0) || filterValues != 1))
4487 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4488 }
4489
4490 /**
4491 * Adapts a target method handle by pre-processing
4492 * some of its arguments, and then calling the target with
4493 * the result of the pre-processing, inserted into the original
4494 * sequence of arguments.
4495 * <p>
4496 * The pre-processing is performed by {@code combiner}, a second method handle.
4497 * Of the arguments passed to the adapter, the first {@code N} arguments
4498 * are copied to the combiner, which is then called.
4499 * (Here, {@code N} is defined as the parameter count of the combiner.)
4500 * After this, control passes to the target, with any result
4501 * from the combiner inserted before the original {@code N} incoming
4502 * arguments.
4503 * <p>
4504 * If the combiner returns a value, the first parameter type of the target
4505 * must be identical with the return type of the combiner, and the next
4506 * {@code N} parameter types of the target must exactly match the parameters
4507 * of the combiner.
4508 * <p>
4509 * If the combiner has a void return, no result will be inserted,
4510 * and the first {@code N} parameter types of the target
4511 * must exactly match the parameters of the combiner.
4512 * <p>
4513 * The resulting adapter is the same type as the target, except that the
4514 * first parameter type is dropped,
4515 * if it corresponds to the result of the combiner.
4516 * <p>
4517 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4518 * that either the combiner or the target does not wish to receive.
4519 * If some of the incoming arguments are destined only for the combiner,
4520 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4521 * arguments will not need to be live on the stack on entry to the
4522 * target.)
4523 * <p><b>Example:</b>
4524 * <blockquote><pre>{@code
4525 import static java.lang.invoke.MethodHandles.*;
4526 import static java.lang.invoke.MethodType.*;
4527 ...
4528 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4529 "println", methodType(void.class, String.class))
4530 .bindTo(System.out);
4531 MethodHandle cat = lookup().findVirtual(String.class,
4532 "concat", methodType(String.class, String.class));
4533 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4534 MethodHandle catTrace = foldArguments(cat, trace);
4535 // also prints "boo":
4536 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4537 * }</pre></blockquote>
4538 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4539 * represents the result type of the {@code target} and resulting adapter.
4540 * {@code V}/{@code v} represent the type and value of the parameter and argument
4541 * of {@code target} that precedes the folding position; {@code V} also is
4542 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4543 * types and values of the {@code N} parameters and arguments at the folding
4544 * position. {@code B}/{@code b} represent the types and values of the
4545 * {@code target} parameters and arguments that follow the folded parameters
4546 * and arguments.
4547 * <blockquote><pre>{@code
4548 * // there are N arguments in A...
4549 * T target(V, A[N]..., B...);
4550 * V combiner(A...);
4551 * T adapter(A... a, B... b) {
4552 * V v = combiner(a...);
4553 * return target(v, a..., b...);
4554 * }
4555 * // and if the combiner has a void return:
4556 * T target2(A[N]..., B...);
4557 * void combiner2(A...);
4558 * T adapter2(A... a, B... b) {
4559 * combiner2(a...);
4560 * return target2(a..., b...);
4561 * }
4562 * }</pre></blockquote>
4563 * <p>
4564 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4565 * variable-arity method handle}, even if the original target method handle was.
4566 * @param target the method handle to invoke after arguments are combined
4567 * @param combiner method handle to call initially on the incoming arguments
4568 * @return method handle which incorporates the specified argument folding logic
4569 * @throws NullPointerException if either argument is null
4570 * @throws IllegalArgumentException if {@code combiner}'s return type
4571 * is non-void and not the same as the first argument type of
4572 * the target, or if the initial {@code N} argument types
4573 * of the target
4574 * (skipping one matching the {@code combiner}'s return type)
4575 * are not identical with the argument types of {@code combiner}
4576 */
4577 public static
4578 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4579 return foldArguments(target, 0, combiner);
4580 }
4581
4582 /**
4583 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4584 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4585 * before the folded arguments.
4586 * <p>
4587 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4588 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4589 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4590 * 0.
4591 *
4592 * @apiNote Example:
4593 * <blockquote><pre>{@code
4594 import static java.lang.invoke.MethodHandles.*;
4595 import static java.lang.invoke.MethodType.*;
4596 ...
4597 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4598 "println", methodType(void.class, String.class))
4599 .bindTo(System.out);
4600 MethodHandle cat = lookup().findVirtual(String.class,
4601 "concat", methodType(String.class, String.class));
4602 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4603 MethodHandle catTrace = foldArguments(cat, 1, trace);
4604 // also prints "jum":
4605 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4606 * }</pre></blockquote>
4607 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4608 * represents the result type of the {@code target} and resulting adapter.
4609 * {@code V}/{@code v} represent the type and value of the parameter and argument
4610 * of {@code target} that precedes the folding position; {@code V} also is
4611 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4612 * types and values of the {@code N} parameters and arguments at the folding
4613 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4614 * and values of the {@code target} parameters and arguments that precede and
4615 * follow the folded parameters and arguments starting at {@code pos},
4616 * respectively.
4617 * <blockquote><pre>{@code
4618 * // there are N arguments in A...
4619 * T target(Z..., V, A[N]..., B...);
4620 * V combiner(A...);
4621 * T adapter(Z... z, A... a, B... b) {
4622 * V v = combiner(a...);
4623 * return target(z..., v, a..., b...);
4624 * }
4625 * // and if the combiner has a void return:
4626 * T target2(Z..., A[N]..., B...);
4627 * void combiner2(A...);
4628 * T adapter2(Z... z, A... a, B... b) {
4629 * combiner2(a...);
4630 * return target2(z..., a..., b...);
4631 * }
4632 * }</pre></blockquote>
4633 * <p>
4634 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4635 * variable-arity method handle}, even if the original target method handle was.
4636 *
4637 * @param target the method handle to invoke after arguments are combined
4638 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4639 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4640 * @param combiner method handle to call initially on the incoming arguments
4641 * @return method handle which incorporates the specified argument folding logic
4642 * @throws NullPointerException if either argument is null
4643 * @throws IllegalArgumentException if either of the following two conditions holds:
4644 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4645 * {@code pos} of the target signature;
4646 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4647 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4648 *
4649 * @see #foldArguments(MethodHandle, MethodHandle)
4650 * @since 9
4651 */
4652 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4653 MethodType targetType = target.type();
4654 MethodType combinerType = combiner.type();
4655 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4656 BoundMethodHandle result = target.rebind();
4657 boolean dropResult = rtype == void.class;
4658 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4659 MethodType newType = targetType;
4660 if (!dropResult) {
4661 newType = newType.dropParameterTypes(pos, pos + 1);
4662 }
4663 result = result.copyWithExtendL(newType, lform, combiner);
4664 return result;
4665 }
4666
4667 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4668 int foldArgs = combinerType.parameterCount();
4669 Class<?> rtype = combinerType.returnType();
4670 int foldVals = rtype == void.class ? 0 : 1;
4671 int afterInsertPos = foldPos + foldVals;
4672 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4673 if (ok) {
4674 for (int i = 0; i < foldArgs; i++) {
4675 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4676 ok = false;
4677 break;
4678 }
4679 }
4680 }
4681 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4682 ok = false;
4683 if (!ok)
4684 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4685 return rtype;
4686 }
4687
4688 /**
4689 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
4690 * of the pre-processing replacing the argument at the given position.
4691 *
4692 * @param target the method handle to invoke after arguments are combined
4693 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
4694 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4695 * @param combiner method handle to call initially on the incoming arguments
4696 * @param argPositions indexes of the target to pick arguments sent to the combiner from
4697 * @return method handle which incorporates the specified argument folding logic
4698 * @throws NullPointerException if either argument is null
4699 * @throws IllegalArgumentException if either of the following two conditions holds:
4700 * (1) {@code combiner}'s return type is not the same as the argument type at position
4701 * {@code pos} of the target signature;
4702 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
4703 * not identical with the argument types of {@code combiner}.
4704 */
4705 /*non-public*/ static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4706 return argumentsWithCombiner(true, target, position, combiner, argPositions);
4707 }
4708
4709 /**
4710 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
4711 * the pre-processing inserted into the original sequence of arguments at the given position.
4712 *
4713 * @param target the method handle to invoke after arguments are combined
4714 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
4715 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4716 * @param combiner method handle to call initially on the incoming arguments
4717 * @param argPositions indexes of the target to pick arguments sent to the combiner from
4718 * @return method handle which incorporates the specified argument folding logic
4719 * @throws NullPointerException if either argument is null
4720 * @throws IllegalArgumentException if either of the following two conditions holds:
4721 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4722 * {@code pos} of the target signature;
4723 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
4724 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
4725 * with the argument types of {@code combiner}.
4726 */
4727 /*non-public*/ static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4728 return argumentsWithCombiner(false, target, position, combiner, argPositions);
4729 }
4730
4731 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
4732 MethodType targetType = target.type();
4733 MethodType combinerType = combiner.type();
4734 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
4735 BoundMethodHandle result = target.rebind();
4736
4737 MethodType newType = targetType;
4738 LambdaForm lform;
4739 if (filter) {
4740 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
4741 } else {
4742 boolean dropResult = rtype == void.class;
4743 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
4744 if (!dropResult) {
4745 newType = newType.dropParameterTypes(position, position + 1);
4746 }
4747 }
4748 result = result.copyWithExtendL(newType, lform, combiner);
4749 return result;
4750 }
4751
4752 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
4753 int combinerArgs = combinerType.parameterCount();
4754 if (argPos.length != combinerArgs) {
4755 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4756 }
4757 Class<?> rtype = combinerType.returnType();
4758
4759 for (int i = 0; i < combinerArgs; i++) {
4760 int arg = argPos[i];
4761 if (arg < 0 || arg > targetType.parameterCount()) {
4762 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4763 }
4764 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4765 throw newIllegalArgumentException("target argument type at position " + arg
4766 + " must match combiner argument type at index " + i + ": " + targetType
4767 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4768 }
4769 }
4770 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
4771 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4772 }
4773 return rtype;
4774 }
4775
4776 /**
4777 * Makes a method handle which adapts a target method handle,
4778 * by guarding it with a test, a boolean-valued method handle.
4779 * If the guard fails, a fallback handle is called instead.
4780 * All three method handles must have the same corresponding
4781 * argument and return types, except that the return type
4782 * of the test must be boolean, and the test is allowed
4783 * to have fewer arguments than the other two method handles.
4784 * <p>
4785 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4786 * represents the uniform result type of the three involved handles;
4787 * {@code A}/{@code a}, the types and values of the {@code target}
4788 * parameters and arguments that are consumed by the {@code test}; and
4789 * {@code B}/{@code b}, those types and values of the {@code target}
4790 * parameters and arguments that are not consumed by the {@code test}.
4791 * <blockquote><pre>{@code
4792 * boolean test(A...);
4793 * T target(A...,B...);
4794 * T fallback(A...,B...);
4795 * T adapter(A... a,B... b) {
4796 * if (test(a...))
4797 * return target(a..., b...);
4798 * else
4799 * return fallback(a..., b...);
4800 * }
4801 * }</pre></blockquote>
4802 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4803 * be modified by execution of the test, and so are passed unchanged
4804 * from the caller to the target or fallback as appropriate.
4805 * @param test method handle used for test, must return boolean
4806 * @param target method handle to call if test passes
4807 * @param fallback method handle to call if test fails
4808 * @return method handle which incorporates the specified if/then/else logic
4809 * @throws NullPointerException if any argument is null
4810 * @throws IllegalArgumentException if {@code test} does not return boolean,
4811 * or if all three method types do not match (with the return
4812 * type of {@code test} changed to match that of the target).
4813 */
4814 public static
4815 MethodHandle guardWithTest(MethodHandle test,
4816 MethodHandle target,
4817 MethodHandle fallback) {
4818 MethodType gtype = test.type();
4819 MethodType ttype = target.type();
4820 MethodType ftype = fallback.type();
4821 if (!ttype.equals(ftype))
4822 throw misMatchedTypes("target and fallback types", ttype, ftype);
4823 if (gtype.returnType() != boolean.class)
4824 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4825 List<Class<?>> targs = ttype.parameterList();
4826 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4827 if (test == null) {
4828 throw misMatchedTypes("target and test types", ttype, gtype);
4829 }
4830 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4831 }
4832
4833 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4834 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4835 }
4836
4837 /**
4838 * Makes a method handle which adapts a target method handle,
4839 * by running it inside an exception handler.
4840 * If the target returns normally, the adapter returns that value.
4841 * If an exception matching the specified type is thrown, the fallback
4842 * handle is called instead on the exception, plus the original arguments.
4843 * <p>
4844 * The target and handler must have the same corresponding
4845 * argument and return types, except that handler may omit trailing arguments
4846 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4847 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4848 * <p>
4849 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4850 * represents the return type of the {@code target} and {@code handler},
4851 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4852 * the types and values of arguments to the resulting handle consumed by
4853 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4854 * resulting handle discarded by {@code handler}.
4855 * <blockquote><pre>{@code
4856 * T target(A..., B...);
4857 * T handler(ExType, A...);
4858 * T adapter(A... a, B... b) {
4859 * try {
4860 * return target(a..., b...);
4861 * } catch (ExType ex) {
4862 * return handler(ex, a...);
4863 * }
4864 * }
4865 * }</pre></blockquote>
4866 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4867 * be modified by execution of the target, and so are passed unchanged
4868 * from the caller to the handler, if the handler is invoked.
4869 * <p>
4870 * The target and handler must return the same type, even if the handler
4871 * always throws. (This might happen, for instance, because the handler
4872 * is simulating a {@code finally} clause).
4873 * To create such a throwing handler, compose the handler creation logic
4874 * with {@link #throwException throwException},
4875 * in order to create a method handle of the correct return type.
4876 * @param target method handle to call
4877 * @param exType the type of exception which the handler will catch
4878 * @param handler method handle to call if a matching exception is thrown
4879 * @return method handle which incorporates the specified try/catch logic
4880 * @throws NullPointerException if any argument is null
4881 * @throws IllegalArgumentException if {@code handler} does not accept
4882 * the given exception type, or if the method handle types do
4883 * not match in their return types and their
4884 * corresponding parameters
4885 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4886 */
4887 public static
4888 MethodHandle catchException(MethodHandle target,
4889 Class<? extends Throwable> exType,
4890 MethodHandle handler) {
4891 MethodType ttype = target.type();
4892 MethodType htype = handler.type();
4893 if (!Throwable.class.isAssignableFrom(exType))
4894 throw new ClassCastException(exType.getName());
4895 if (htype.parameterCount() < 1 ||
4896 !htype.parameterType(0).isAssignableFrom(exType))
4897 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4898 if (htype.returnType() != ttype.returnType())
4899 throw misMatchedTypes("target and handler return types", ttype, htype);
4900 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4901 if (handler == null) {
4902 throw misMatchedTypes("target and handler types", ttype, htype);
4903 }
4904 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4905 }
4906
4907 /**
4908 * Produces a method handle which will throw exceptions of the given {@code exType}.
4909 * The method handle will accept a single argument of {@code exType},
4910 * and immediately throw it as an exception.
4911 * The method type will nominally specify a return of {@code returnType}.
4912 * The return type may be anything convenient: It doesn't matter to the
4913 * method handle's behavior, since it will never return normally.
4914 * @param returnType the return type of the desired method handle
4915 * @param exType the parameter type of the desired method handle
4916 * @return method handle which can throw the given exceptions
4917 * @throws NullPointerException if either argument is null
4918 */
4919 public static
4920 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4921 if (!Throwable.class.isAssignableFrom(exType))
4922 throw new ClassCastException(exType.getName());
4923 return MethodHandleImpl.throwException(methodType(returnType, exType));
4924 }
4925
4926 /**
4927 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4928 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4929 * delivers the loop's result, which is the return value of the resulting handle.
4930 * <p>
4931 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4932 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4933 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4934 * terms of method handles, each clause will specify up to four independent actions:<ul>
4935 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4936 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4937 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4938 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4939 * </ul>
4940 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4941 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4942 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4943 * <p>
4944 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4945 * this case. See below for a detailed description.
4946 * <p>
4947 * <em>Parameters optional everywhere:</em>
4948 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4949 * As an exception, the init functions cannot take any {@code v} parameters,
4950 * because those values are not yet computed when the init functions are executed.
4951 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4952 * In fact, any clause function may take no arguments at all.
4953 * <p>
4954 * <em>Loop parameters:</em>
4955 * A clause function may take all the iteration variable values it is entitled to, in which case
4956 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4957 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4958 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4959 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4960 * init function is automatically a loop parameter {@code a}.)
4961 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4962 * These loop parameters act as loop-invariant values visible across the whole loop.
4963 * <p>
4964 * <em>Parameters visible everywhere:</em>
4965 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4966 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4967 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4968 * Most clause functions will not need all of this information, but they will be formally connected to it
4969 * as if by {@link #dropArguments}.
4970 * <a id="astar"></a>
4971 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4972 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4973 * In that notation, the general form of an init function parameter list
4974 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4975 * <p>
4976 * <em>Checking clause structure:</em>
4977 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4978 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4979 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4980 * met by the inputs to the loop combinator.
4981 * <p>
4982 * <em>Effectively identical sequences:</em>
4983 * <a id="effid"></a>
4984 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4985 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4986 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4987 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4988 * that longest list.
4989 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4990 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4991 * <p>
4992 * <em>Step 0: Determine clause structure.</em><ol type="a">
4993 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4994 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4995 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4996 * four. Padding takes place by appending elements to the array.
4997 * <li>Clauses with all {@code null}s are disregarded.
4998 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4999 * </ol>
5000 * <p>
5001 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
5002 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
5003 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
5004 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
5005 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
5006 * iteration variable type.
5007 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
5008 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
5009 * </ol>
5010 * <p>
5011 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
5012 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
5013 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
5014 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
5015 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
5016 * (These types will checked in step 2, along with all the clause function types.)
5017 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
5018 * <li>All of the collected parameter lists must be effectively identical.
5019 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
5020 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
5021 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
5022 * the "internal parameter list".
5023 * </ul>
5024 * <p>
5025 * <em>Step 1C: Determine loop return type.</em><ol type="a">
5026 * <li>Examine fini function return types, disregarding omitted fini functions.
5027 * <li>If there are no fini functions, the loop return type is {@code void}.
5028 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
5029 * type.
5030 * </ol>
5031 * <p>
5032 * <em>Step 1D: Check other types.</em><ol type="a">
5033 * <li>There must be at least one non-omitted pred function.
5034 * <li>Every non-omitted pred function must have a {@code boolean} return type.
5035 * </ol>
5036 * <p>
5037 * <em>Step 2: Determine parameter lists.</em><ol type="a">
5038 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
5039 * <li>The parameter list for init functions will be adjusted to the external parameter list.
5040 * (Note that their parameter lists are already effectively identical to this list.)
5041 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
5042 * effectively identical to the internal parameter list {@code (V... A...)}.
5043 * </ol>
5044 * <p>
5045 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
5046 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
5047 * type.
5048 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
5049 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
5050 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
5051 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
5052 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
5053 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
5054 * loop return type.
5055 * </ol>
5056 * <p>
5057 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
5058 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
5059 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
5060 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
5061 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
5062 * pad out the end of the list.
5063 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
5064 * </ol>
5065 * <p>
5066 * <em>Final observations.</em><ol type="a">
5067 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
5068 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
5069 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
5070 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
5071 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
5072 * <li>Each pair of init and step functions agrees in their return type {@code V}.
5073 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
5074 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
5075 * </ol>
5076 * <p>
5077 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
5078 * <ul>
5079 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
5080 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
5081 * (Only one {@code Pn} has to be non-{@code null}.)
5082 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
5083 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
5084 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
5085 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
5086 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
5087 * the resulting loop handle's parameter types {@code (A...)}.
5088 * </ul>
5089 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
5090 * which is natural if most of the loop computation happens in the steps. For some loops,
5091 * the burden of computation might be heaviest in the pred functions, and so the pred functions
5092 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
5093 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
5094 * where the init functions will need the extra parameters. For such reasons, the rules for
5095 * determining these parameters are as symmetric as possible, across all clause parts.
5096 * In general, the loop parameters function as common invariant values across the whole
5097 * loop, while the iteration variables function as common variant values, or (if there is
5098 * no step function) as internal loop invariant temporaries.
5099 * <p>
5100 * <em>Loop execution.</em><ol type="a">
5101 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
5102 * every clause function. These locals are loop invariant.
5103 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
5104 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
5105 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
5106 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
5107 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
5108 * (in argument order).
5109 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
5110 * returns {@code false}.
5111 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
5112 * sequence {@code (v...)} of loop variables.
5113 * The updated value is immediately visible to all subsequent function calls.
5114 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
5115 * (of type {@code R}) is returned from the loop as a whole.
5116 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
5117 * except by throwing an exception.
5118 * </ol>
5119 * <p>
5120 * <em>Usage tips.</em>
5121 * <ul>
5122 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
5123 * sometimes a step function only needs to observe the current value of its own variable.
5124 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
5125 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
5126 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
5127 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
5128 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
5129 * <li>If some of the clause functions are virtual methods on an instance, the instance
5130 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
5131 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
5132 * will be the first iteration variable value, and it will be easy to use virtual
5133 * methods as clause parts, since all of them will take a leading instance reference matching that value.
5134 * </ul>
5135 * <p>
5136 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
5137 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
5138 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
5139 * <blockquote><pre>{@code
5140 * V... init...(A...);
5141 * boolean pred...(V..., A...);
5142 * V... step...(V..., A...);
5143 * R fini...(V..., A...);
5144 * R loop(A... a) {
5145 * V... v... = init...(a...);
5146 * for (;;) {
5147 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
5148 * v = s(v..., a...);
5149 * if (!p(v..., a...)) {
5150 * return f(v..., a...);
5151 * }
5152 * }
5153 * }
5154 * }
5155 * }</pre></blockquote>
5156 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
5157 * to their full length, even though individual clause functions may neglect to take them all.
5158 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
5159 *
5160 * @apiNote Example:
5161 * <blockquote><pre>{@code
5162 * // iterative implementation of the factorial function as a loop handle
5163 * static int one(int k) { return 1; }
5164 * static int inc(int i, int acc, int k) { return i + 1; }
5165 * static int mult(int i, int acc, int k) { return i * acc; }
5166 * static boolean pred(int i, int acc, int k) { return i < k; }
5167 * static int fin(int i, int acc, int k) { return acc; }
5168 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5169 * // null initializer for counter, should initialize to 0
5170 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5171 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5172 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5173 * assertEquals(120, loop.invoke(5));
5174 * }</pre></blockquote>
5175 * The same example, dropping arguments and using combinators:
5176 * <blockquote><pre>{@code
5177 * // simplified implementation of the factorial function as a loop handle
5178 * static int inc(int i) { return i + 1; } // drop acc, k
5179 * static int mult(int i, int acc) { return i * acc; } //drop k
5180 * static boolean cmp(int i, int k) { return i < k; }
5181 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
5182 * // null initializer for counter, should initialize to 0
5183 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5184 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
5185 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
5186 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5187 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5188 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
5189 * assertEquals(720, loop.invoke(6));
5190 * }</pre></blockquote>
5191 * A similar example, using a helper object to hold a loop parameter:
5192 * <blockquote><pre>{@code
5193 * // instance-based implementation of the factorial function as a loop handle
5194 * static class FacLoop {
5195 * final int k;
5196 * FacLoop(int k) { this.k = k; }
5197 * int inc(int i) { return i + 1; }
5198 * int mult(int i, int acc) { return i * acc; }
5199 * boolean pred(int i) { return i < k; }
5200 * int fin(int i, int acc) { return acc; }
5201 * }
5202 * // assume MH_FacLoop is a handle to the constructor
5203 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
5204 * // null initializer for counter, should initialize to 0
5205 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
5206 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
5207 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
5208 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
5209 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
5210 * assertEquals(5040, loop.invoke(7));
5211 * }</pre></blockquote>
5212 *
5213 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
5214 *
5215 * @return a method handle embodying the looping behavior as defined by the arguments.
5216 *
5217 * @throws IllegalArgumentException in case any of the constraints described above is violated.
5218 *
5219 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
5220 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5221 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
5222 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
5223 * @since 9
5224 */
5225 public static MethodHandle loop(MethodHandle[]... clauses) {
5226 // Step 0: determine clause structure.
5227 loopChecks0(clauses);
5228
5229 List<MethodHandle> init = new ArrayList<>();
5230 List<MethodHandle> step = new ArrayList<>();
5231 List<MethodHandle> pred = new ArrayList<>();
5232 List<MethodHandle> fini = new ArrayList<>();
5233
5234 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
5235 init.add(clause[0]); // all clauses have at least length 1
5236 step.add(clause.length <= 1 ? null : clause[1]);
5237 pred.add(clause.length <= 2 ? null : clause[2]);
5238 fini.add(clause.length <= 3 ? null : clause[3]);
5239 });
5240
5241 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
5242 final int nclauses = init.size();
5243
5244 // Step 1A: determine iteration variables (V...).
5245 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
5246 for (int i = 0; i < nclauses; ++i) {
5247 MethodHandle in = init.get(i);
5248 MethodHandle st = step.get(i);
5249 if (in == null && st == null) {
5250 iterationVariableTypes.add(void.class);
5251 } else if (in != null && st != null) {
5252 loopChecks1a(i, in, st);
5253 iterationVariableTypes.add(in.type().returnType());
5254 } else {
5255 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
5256 }
5257 }
5258 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
5259 collect(Collectors.toList());
5260
5261 // Step 1B: determine loop parameters (A...).
5262 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
5263 loopChecks1b(init, commonSuffix);
5264
5265 // Step 1C: determine loop return type.
5266 // Step 1D: check other types.
5267 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
5268 map(MethodType::returnType).findFirst().orElse(void.class);
5269 loopChecks1cd(pred, fini, loopReturnType);
5270
5271 // Step 2: determine parameter lists.
5272 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
5273 commonParameterSequence.addAll(commonSuffix);
5274 loopChecks2(step, pred, fini, commonParameterSequence);
5275
5276 // Step 3: fill in omitted functions.
5277 for (int i = 0; i < nclauses; ++i) {
5278 Class<?> t = iterationVariableTypes.get(i);
5279 if (init.get(i) == null) {
5280 init.set(i, empty(methodType(t, commonSuffix)));
5281 }
5282 if (step.get(i) == null) {
5283 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
5284 }
5285 if (pred.get(i) == null) {
5286 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
5287 }
5288 if (fini.get(i) == null) {
5289 fini.set(i, empty(methodType(t, commonParameterSequence)));
5290 }
5291 }
5292
5293 // Step 4: fill in missing parameter types.
5294 // Also convert all handles to fixed-arity handles.
5295 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
5296 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
5297 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
5298 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
5299
5300 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
5301 allMatch(pl -> pl.equals(commonSuffix));
5302 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
5303 allMatch(pl -> pl.equals(commonParameterSequence));
5304
5305 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
5306 }
5307
5308 private static void loopChecks0(MethodHandle[][] clauses) {
5309 if (clauses == null || clauses.length == 0) {
5310 throw newIllegalArgumentException("null or no clauses passed");
5311 }
5312 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
5313 throw newIllegalArgumentException("null clauses are not allowed");
5314 }
5315 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
5316 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
5317 }
5318 }
5319
5320 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
5321 if (in.type().returnType() != st.type().returnType()) {
5322 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
5323 st.type().returnType());
5324 }
5325 }
5326
5327 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
5328 final List<Class<?>> empty = List.of();
5329 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
5330 // take only those that can contribute to a common suffix because they are longer than the prefix
5331 map(MethodHandle::type).
5332 filter(t -> t.parameterCount() > skipSize).
5333 map(MethodType::parameterList).
5334 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5335 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
5336 }
5337
5338 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
5339 final List<Class<?>> empty = List.of();
5340 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
5341 }
5342
5343 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
5344 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
5345 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
5346 return longestParameterList(Arrays.asList(longest1, longest2));
5347 }
5348
5349 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
5350 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
5351 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
5352 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
5353 " (common suffix: " + commonSuffix + ")");
5354 }
5355 }
5356
5357 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
5358 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5359 anyMatch(t -> t != loopReturnType)) {
5360 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
5361 loopReturnType + ")");
5362 }
5363
5364 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5365 throw newIllegalArgumentException("no predicate found", pred);
5366 }
5367 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5368 anyMatch(t -> t != boolean.class)) {
5369 throw newIllegalArgumentException("predicates must have boolean return type", pred);
5370 }
5371 }
5372
5373 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5374 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5375 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
5376 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5377 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5378 }
5379 }
5380
5381 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
5382 return hs.stream().map(h -> {
5383 int pc = h.type().parameterCount();
5384 int tpsize = targetParams.size();
5385 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
5386 }).collect(Collectors.toList());
5387 }
5388
5389 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
5390 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
5391 }
5392
5393 /**
5394 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
5395 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5396 * <p>
5397 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5398 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
5399 * evaluates to {@code true}).
5400 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
5401 * <p>
5402 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5403 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5404 * and updated with the value returned from its invocation. The result of loop execution will be
5405 * the final value of the additional loop-local variable (if present).
5406 * <p>
5407 * The following rules hold for these argument handles:<ul>
5408 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5409 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5410 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5411 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5412 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5413 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5414 * It will constrain the parameter lists of the other loop parts.
5415 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5416 * list {@code (A...)} is called the <em>external parameter list</em>.
5417 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5418 * additional state variable of the loop.
5419 * The body must both accept and return a value of this type {@code V}.
5420 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5421 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5422 * <a href="MethodHandles.html#effid">effectively identical</a>
5423 * to the external parameter list {@code (A...)}.
5424 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5425 * {@linkplain #empty default value}.
5426 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5427 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5428 * effectively identical to the internal parameter list.
5429 * </ul>
5430 * <p>
5431 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5432 * <li>The loop handle's result type is the result type {@code V} of the body.
5433 * <li>The loop handle's parameter types are the types {@code (A...)},
5434 * from the external parameter list.
5435 * </ul>
5436 * <p>
5437 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5438 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5439 * passed to the loop.
5440 * <blockquote><pre>{@code
5441 * V init(A...);
5442 * boolean pred(V, A...);
5443 * V body(V, A...);
5444 * V whileLoop(A... a...) {
5445 * V v = init(a...);
5446 * while (pred(v, a...)) {
5447 * v = body(v, a...);
5448 * }
5449 * return v;
5450 * }
5451 * }</pre></blockquote>
5452 *
5453 * @apiNote Example:
5454 * <blockquote><pre>{@code
5455 * // implement the zip function for lists as a loop handle
5456 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5457 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5458 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5459 * zip.add(a.next());
5460 * zip.add(b.next());
5461 * return zip;
5462 * }
5463 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5464 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5465 * List<String> a = Arrays.asList("a", "b", "c", "d");
5466 * List<String> b = Arrays.asList("e", "f", "g", "h");
5467 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5468 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5469 * }</pre></blockquote>
5470 *
5471 *
5472 * @apiNote The implementation of this method can be expressed as follows:
5473 * <blockquote><pre>{@code
5474 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5475 * MethodHandle fini = (body.type().returnType() == void.class
5476 * ? null : identity(body.type().returnType()));
5477 * MethodHandle[]
5478 * checkExit = { null, null, pred, fini },
5479 * varBody = { init, body };
5480 * return loop(checkExit, varBody);
5481 * }
5482 * }</pre></blockquote>
5483 *
5484 * @param init optional initializer, providing the initial value of the loop variable.
5485 * May be {@code null}, implying a default initial value. See above for other constraints.
5486 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5487 * above for other constraints.
5488 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5489 * See above for other constraints.
5490 *
5491 * @return a method handle implementing the {@code while} loop as described by the arguments.
5492 * @throws IllegalArgumentException if the rules for the arguments are violated.
5493 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5494 *
5495 * @see #loop(MethodHandle[][])
5496 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5497 * @since 9
5498 */
5499 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5500 whileLoopChecks(init, pred, body);
5501 MethodHandle fini = identityOrVoid(body.type().returnType());
5502 MethodHandle[] checkExit = { null, null, pred, fini };
5503 MethodHandle[] varBody = { init, body };
5504 return loop(checkExit, varBody);
5505 }
5506
5507 /**
5508 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5509 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5510 * <p>
5511 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5512 * method will, in each iteration, first execute its body and then evaluate the predicate.
5513 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5514 * <p>
5515 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5516 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5517 * and updated with the value returned from its invocation. The result of loop execution will be
5518 * the final value of the additional loop-local variable (if present).
5519 * <p>
5520 * The following rules hold for these argument handles:<ul>
5521 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5522 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5523 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5524 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5525 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5526 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5527 * It will constrain the parameter lists of the other loop parts.
5528 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5529 * list {@code (A...)} is called the <em>external parameter list</em>.
5530 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5531 * additional state variable of the loop.
5532 * The body must both accept and return a value of this type {@code V}.
5533 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5534 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5535 * <a href="MethodHandles.html#effid">effectively identical</a>
5536 * to the external parameter list {@code (A...)}.
5537 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5538 * {@linkplain #empty default value}.
5539 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5540 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5541 * effectively identical to the internal parameter list.
5542 * </ul>
5543 * <p>
5544 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5545 * <li>The loop handle's result type is the result type {@code V} of the body.
5546 * <li>The loop handle's parameter types are the types {@code (A...)},
5547 * from the external parameter list.
5548 * </ul>
5549 * <p>
5550 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5551 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5552 * passed to the loop.
5553 * <blockquote><pre>{@code
5554 * V init(A...);
5555 * boolean pred(V, A...);
5556 * V body(V, A...);
5557 * V doWhileLoop(A... a...) {
5558 * V v = init(a...);
5559 * do {
5560 * v = body(v, a...);
5561 * } while (pred(v, a...));
5562 * return v;
5563 * }
5564 * }</pre></blockquote>
5565 *
5566 * @apiNote Example:
5567 * <blockquote><pre>{@code
5568 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5569 * static int zero(int limit) { return 0; }
5570 * static int step(int i, int limit) { return i + 1; }
5571 * static boolean pred(int i, int limit) { return i < limit; }
5572 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5573 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5574 * assertEquals(23, loop.invoke(23));
5575 * }</pre></blockquote>
5576 *
5577 *
5578 * @apiNote The implementation of this method can be expressed as follows:
5579 * <blockquote><pre>{@code
5580 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5581 * MethodHandle fini = (body.type().returnType() == void.class
5582 * ? null : identity(body.type().returnType()));
5583 * MethodHandle[] clause = { init, body, pred, fini };
5584 * return loop(clause);
5585 * }
5586 * }</pre></blockquote>
5587 *
5588 * @param init optional initializer, providing the initial value of the loop variable.
5589 * May be {@code null}, implying a default initial value. See above for other constraints.
5590 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5591 * See above for other constraints.
5592 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5593 * above for other constraints.
5594 *
5595 * @return a method handle implementing the {@code while} loop as described by the arguments.
5596 * @throws IllegalArgumentException if the rules for the arguments are violated.
5597 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5598 *
5599 * @see #loop(MethodHandle[][])
5600 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5601 * @since 9
5602 */
5603 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5604 whileLoopChecks(init, pred, body);
5605 MethodHandle fini = identityOrVoid(body.type().returnType());
5606 MethodHandle[] clause = {init, body, pred, fini };
5607 return loop(clause);
5608 }
5609
5610 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5611 Objects.requireNonNull(pred);
5612 Objects.requireNonNull(body);
5613 MethodType bodyType = body.type();
5614 Class<?> returnType = bodyType.returnType();
5615 List<Class<?>> innerList = bodyType.parameterList();
5616 List<Class<?>> outerList = innerList;
5617 if (returnType == void.class) {
5618 // OK
5619 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5620 // leading V argument missing => error
5621 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5622 throw misMatchedTypes("body function", bodyType, expected);
5623 } else {
5624 outerList = innerList.subList(1, innerList.size());
5625 }
5626 MethodType predType = pred.type();
5627 if (predType.returnType() != boolean.class ||
5628 !predType.effectivelyIdenticalParameters(0, innerList)) {
5629 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5630 }
5631 if (init != null) {
5632 MethodType initType = init.type();
5633 if (initType.returnType() != returnType ||
5634 !initType.effectivelyIdenticalParameters(0, outerList)) {
5635 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5636 }
5637 }
5638 }
5639
5640 /**
5641 * Constructs a loop that runs a given number of iterations.
5642 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5643 * <p>
5644 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5645 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5646 * It will be initialized to 0 and incremented by 1 in each iteration.
5647 * <p>
5648 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5649 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5650 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5651 * <p>
5652 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5653 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5654 * iteration variable.
5655 * The result of the loop handle execution will be the final {@code V} value of that variable
5656 * (or {@code void} if there is no {@code V} variable).
5657 * <p>
5658 * The following rules hold for the argument handles:<ul>
5659 * <li>The {@code iterations} handle must not be {@code null}, and must return
5660 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5661 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5662 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5663 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5664 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5665 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5666 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5667 * of types called the <em>internal parameter list</em>.
5668 * It will constrain the parameter lists of the other loop parts.
5669 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5670 * with no additional {@code A} types, then the internal parameter list is extended by
5671 * the argument types {@code A...} of the {@code iterations} handle.
5672 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5673 * list {@code (A...)} is called the <em>external parameter list</em>.
5674 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5675 * additional state variable of the loop.
5676 * The body must both accept a leading parameter and return a value of this type {@code V}.
5677 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5678 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5679 * <a href="MethodHandles.html#effid">effectively identical</a>
5680 * to the external parameter list {@code (A...)}.
5681 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5682 * {@linkplain #empty default value}.
5683 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5684 * effectively identical to the external parameter list {@code (A...)}.
5685 * </ul>
5686 * <p>
5687 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5688 * <li>The loop handle's result type is the result type {@code V} of the body.
5689 * <li>The loop handle's parameter types are the types {@code (A...)},
5690 * from the external parameter list.
5691 * </ul>
5692 * <p>
5693 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5694 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5695 * arguments passed to the loop.
5696 * <blockquote><pre>{@code
5697 * int iterations(A...);
5698 * V init(A...);
5699 * V body(V, int, A...);
5700 * V countedLoop(A... a...) {
5701 * int end = iterations(a...);
5702 * V v = init(a...);
5703 * for (int i = 0; i < end; ++i) {
5704 * v = body(v, i, a...);
5705 * }
5706 * return v;
5707 * }
5708 * }</pre></blockquote>
5709 *
5710 * @apiNote Example with a fully conformant body method:
5711 * <blockquote><pre>{@code
5712 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5713 * // => a variation on a well known theme
5714 * static String step(String v, int counter, String init) { return "na " + v; }
5715 * // assume MH_step is a handle to the method above
5716 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5717 * MethodHandle start = MethodHandles.identity(String.class);
5718 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5719 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5720 * }</pre></blockquote>
5721 *
5722 * @apiNote Example with the simplest possible body method type,
5723 * and passing the number of iterations to the loop invocation:
5724 * <blockquote><pre>{@code
5725 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5726 * // => a variation on a well known theme
5727 * static String step(String v, int counter ) { return "na " + v; }
5728 * // assume MH_step is a handle to the method above
5729 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5730 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5731 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5732 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5733 * }</pre></blockquote>
5734 *
5735 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5736 * as loop parameters:
5737 * <blockquote><pre>{@code
5738 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5739 * // => a variation on a well known theme
5740 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5741 * // assume MH_step is a handle to the method above
5742 * MethodHandle count = MethodHandles.identity(int.class);
5743 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5744 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5745 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5746 * }</pre></blockquote>
5747 *
5748 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5749 * to enforce a loop type:
5750 * <blockquote><pre>{@code
5751 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5752 * // => a variation on a well known theme
5753 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5754 * // assume MH_step is a handle to the method above
5755 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5756 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5757 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5758 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5759 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5760 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5761 * }</pre></blockquote>
5762 *
5763 * @apiNote The implementation of this method can be expressed as follows:
5764 * <blockquote><pre>{@code
5765 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5766 * return countedLoop(empty(iterations.type()), iterations, init, body);
5767 * }
5768 * }</pre></blockquote>
5769 *
5770 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5771 * result type must be {@code int}. See above for other constraints.
5772 * @param init optional initializer, providing the initial value of the loop variable.
5773 * May be {@code null}, implying a default initial value. See above for other constraints.
5774 * @param body body of the loop, which may not be {@code null}.
5775 * It controls the loop parameters and result type in the standard case (see above for details).
5776 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5777 * and may accept any number of additional types.
5778 * See above for other constraints.
5779 *
5780 * @return a method handle representing the loop.
5781 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5782 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5783 *
5784 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5785 * @since 9
5786 */
5787 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5788 return countedLoop(empty(iterations.type()), iterations, init, body);
5789 }
5790
5791 /**
5792 * Constructs a loop that counts over a range of numbers.
5793 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5794 * <p>
5795 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5796 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5797 * values of the loop counter.
5798 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5799 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5800 * <p>
5801 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5802 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5803 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5804 * <p>
5805 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5806 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5807 * iteration variable.
5808 * The result of the loop handle execution will be the final {@code V} value of that variable
5809 * (or {@code void} if there is no {@code V} variable).
5810 * <p>
5811 * The following rules hold for the argument handles:<ul>
5812 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5813 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5814 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5815 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5816 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5817 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5818 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5819 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5820 * of types called the <em>internal parameter list</em>.
5821 * It will constrain the parameter lists of the other loop parts.
5822 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5823 * with no additional {@code A} types, then the internal parameter list is extended by
5824 * the argument types {@code A...} of the {@code end} handle.
5825 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5826 * list {@code (A...)} is called the <em>external parameter list</em>.
5827 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5828 * additional state variable of the loop.
5829 * The body must both accept a leading parameter and return a value of this type {@code V}.
5830 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5831 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5832 * <a href="MethodHandles.html#effid">effectively identical</a>
5833 * to the external parameter list {@code (A...)}.
5834 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5835 * {@linkplain #empty default value}.
5836 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5837 * effectively identical to the external parameter list {@code (A...)}.
5838 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5839 * to the external parameter list.
5840 * </ul>
5841 * <p>
5842 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5843 * <li>The loop handle's result type is the result type {@code V} of the body.
5844 * <li>The loop handle's parameter types are the types {@code (A...)},
5845 * from the external parameter list.
5846 * </ul>
5847 * <p>
5848 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5849 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5850 * arguments passed to the loop.
5851 * <blockquote><pre>{@code
5852 * int start(A...);
5853 * int end(A...);
5854 * V init(A...);
5855 * V body(V, int, A...);
5856 * V countedLoop(A... a...) {
5857 * int e = end(a...);
5858 * int s = start(a...);
5859 * V v = init(a...);
5860 * for (int i = s; i < e; ++i) {
5861 * v = body(v, i, a...);
5862 * }
5863 * return v;
5864 * }
5865 * }</pre></blockquote>
5866 *
5867 * @apiNote The implementation of this method can be expressed as follows:
5868 * <blockquote><pre>{@code
5869 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5870 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5871 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5872 * // the following semantics:
5873 * // MH_increment: (int limit, int counter) -> counter + 1
5874 * // MH_predicate: (int limit, int counter) -> counter < limit
5875 * Class<?> counterType = start.type().returnType(); // int
5876 * Class<?> returnType = body.type().returnType();
5877 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5878 * if (returnType != void.class) { // ignore the V variable
5879 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5880 * pred = dropArguments(pred, 1, returnType); // ditto
5881 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5882 * }
5883 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5884 * MethodHandle[]
5885 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5886 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5887 * indexVar = { start, incr }; // i = start(); i = i + 1
5888 * return loop(loopLimit, bodyClause, indexVar);
5889 * }
5890 * }</pre></blockquote>
5891 *
5892 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5893 * See above for other constraints.
5894 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5895 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5896 * @param init optional initializer, providing the initial value of the loop variable.
5897 * May be {@code null}, implying a default initial value. See above for other constraints.
5898 * @param body body of the loop, which may not be {@code null}.
5899 * It controls the loop parameters and result type in the standard case (see above for details).
5900 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5901 * and may accept any number of additional types.
5902 * See above for other constraints.
5903 *
5904 * @return a method handle representing the loop.
5905 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5906 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5907 *
5908 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5909 * @since 9
5910 */
5911 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5912 countedLoopChecks(start, end, init, body);
5913 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5914 Class<?> limitType = end.type().returnType(); // yes, int again
5915 Class<?> returnType = body.type().returnType();
5916 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5917 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5918 MethodHandle retv = null;
5919 if (returnType != void.class) {
5920 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5921 pred = dropArguments(pred, 1, returnType); // ditto
5922 retv = dropArguments(identity(returnType), 0, counterType);
5923 }
5924 body = dropArguments(body, 0, counterType); // ignore the limit variable
5925 MethodHandle[]
5926 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5927 bodyClause = { init, body }, // v = init(); v = body(v, i)
5928 indexVar = { start, incr }; // i = start(); i = i + 1
5929 return loop(loopLimit, bodyClause, indexVar);
5930 }
5931
5932 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5933 Objects.requireNonNull(start);
5934 Objects.requireNonNull(end);
5935 Objects.requireNonNull(body);
5936 Class<?> counterType = start.type().returnType();
5937 if (counterType != int.class) {
5938 MethodType expected = start.type().changeReturnType(int.class);
5939 throw misMatchedTypes("start function", start.type(), expected);
5940 } else if (end.type().returnType() != counterType) {
5941 MethodType expected = end.type().changeReturnType(counterType);
5942 throw misMatchedTypes("end function", end.type(), expected);
5943 }
5944 MethodType bodyType = body.type();
5945 Class<?> returnType = bodyType.returnType();
5946 List<Class<?>> innerList = bodyType.parameterList();
5947 // strip leading V value if present
5948 int vsize = (returnType == void.class ? 0 : 1);
5949 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5950 // argument list has no "V" => error
5951 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5952 throw misMatchedTypes("body function", bodyType, expected);
5953 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5954 // missing I type => error
5955 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5956 throw misMatchedTypes("body function", bodyType, expected);
5957 }
5958 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5959 if (outerList.isEmpty()) {
5960 // special case; take lists from end handle
5961 outerList = end.type().parameterList();
5962 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5963 }
5964 MethodType expected = methodType(counterType, outerList);
5965 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5966 throw misMatchedTypes("start parameter types", start.type(), expected);
5967 }
5968 if (end.type() != start.type() &&
5969 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5970 throw misMatchedTypes("end parameter types", end.type(), expected);
5971 }
5972 if (init != null) {
5973 MethodType initType = init.type();
5974 if (initType.returnType() != returnType ||
5975 !initType.effectivelyIdenticalParameters(0, outerList)) {
5976 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5977 }
5978 }
5979 }
5980
5981 /**
5982 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5983 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5984 * <p>
5985 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5986 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5987 * <p>
5988 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5989 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5990 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5991 * <p>
5992 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5993 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5994 * iteration variable.
5995 * The result of the loop handle execution will be the final {@code V} value of that variable
5996 * (or {@code void} if there is no {@code V} variable).
5997 * <p>
5998 * The following rules hold for the argument handles:<ul>
5999 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6000 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
6001 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6002 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
6003 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
6004 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
6005 * of types called the <em>internal parameter list</em>.
6006 * It will constrain the parameter lists of the other loop parts.
6007 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
6008 * with no additional {@code A} types, then the internal parameter list is extended by
6009 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
6010 * single type {@code Iterable} is added and constitutes the {@code A...} list.
6011 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
6012 * list {@code (A...)} is called the <em>external parameter list</em>.
6013 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6014 * additional state variable of the loop.
6015 * The body must both accept a leading parameter and return a value of this type {@code V}.
6016 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6017 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6018 * <a href="MethodHandles.html#effid">effectively identical</a>
6019 * to the external parameter list {@code (A...)}.
6020 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6021 * {@linkplain #empty default value}.
6022 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
6023 * type {@code java.util.Iterator} or a subtype thereof.
6024 * The iterator it produces when the loop is executed will be assumed
6025 * to yield values which can be converted to type {@code T}.
6026 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
6027 * effectively identical to the external parameter list {@code (A...)}.
6028 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
6029 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
6030 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
6031 * handle parameter is adjusted to accept the leading {@code A} type, as if by
6032 * the {@link MethodHandle#asType asType} conversion method.
6033 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
6034 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
6035 * </ul>
6036 * <p>
6037 * The type {@code T} may be either a primitive or reference.
6038 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
6039 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
6040 * as if by the {@link MethodHandle#asType asType} conversion method.
6041 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
6042 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
6043 * <p>
6044 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6045 * <li>The loop handle's result type is the result type {@code V} of the body.
6046 * <li>The loop handle's parameter types are the types {@code (A...)},
6047 * from the external parameter list.
6048 * </ul>
6049 * <p>
6050 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6051 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
6052 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
6053 * <blockquote><pre>{@code
6054 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
6055 * V init(A...);
6056 * V body(V,T,A...);
6057 * V iteratedLoop(A... a...) {
6058 * Iterator<T> it = iterator(a...);
6059 * V v = init(a...);
6060 * while (it.hasNext()) {
6061 * T t = it.next();
6062 * v = body(v, t, a...);
6063 * }
6064 * return v;
6065 * }
6066 * }</pre></blockquote>
6067 *
6068 * @apiNote Example:
6069 * <blockquote><pre>{@code
6070 * // get an iterator from a list
6071 * static List<String> reverseStep(List<String> r, String e) {
6072 * r.add(0, e);
6073 * return r;
6074 * }
6075 * static List<String> newArrayList() { return new ArrayList<>(); }
6076 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
6077 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
6078 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
6079 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
6080 * assertEquals(reversedList, (List<String>) loop.invoke(list));
6081 * }</pre></blockquote>
6082 *
6083 * @apiNote The implementation of this method can be expressed approximately as follows:
6084 * <blockquote><pre>{@code
6085 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6086 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
6087 * Class<?> returnType = body.type().returnType();
6088 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6089 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
6090 * MethodHandle retv = null, step = body, startIter = iterator;
6091 * if (returnType != void.class) {
6092 * // the simple thing first: in (I V A...), drop the I to get V
6093 * retv = dropArguments(identity(returnType), 0, Iterator.class);
6094 * // body type signature (V T A...), internal loop types (I V A...)
6095 * step = swapArguments(body, 0, 1); // swap V <-> T
6096 * }
6097 * if (startIter == null) startIter = MH_getIter;
6098 * MethodHandle[]
6099 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
6100 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
6101 * return loop(iterVar, bodyClause);
6102 * }
6103 * }</pre></blockquote>
6104 *
6105 * @param iterator an optional handle to return the iterator to start the loop.
6106 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
6107 * See above for other constraints.
6108 * @param init optional initializer, providing the initial value of the loop variable.
6109 * May be {@code null}, implying a default initial value. See above for other constraints.
6110 * @param body body of the loop, which may not be {@code null}.
6111 * It controls the loop parameters and result type in the standard case (see above for details).
6112 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
6113 * and may accept any number of additional types.
6114 * See above for other constraints.
6115 *
6116 * @return a method handle embodying the iteration loop functionality.
6117 * @throws NullPointerException if the {@code body} handle is {@code null}.
6118 * @throws IllegalArgumentException if any argument violates the above requirements.
6119 *
6120 * @since 9
6121 */
6122 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6123 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
6124 Class<?> returnType = body.type().returnType();
6125 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
6126 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
6127 MethodHandle startIter;
6128 MethodHandle nextVal;
6129 {
6130 MethodType iteratorType;
6131 if (iterator == null) {
6132 // derive argument type from body, if available, else use Iterable
6133 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
6134 iteratorType = startIter.type().changeParameterType(0, iterableType);
6135 } else {
6136 // force return type to the internal iterator class
6137 iteratorType = iterator.type().changeReturnType(Iterator.class);
6138 startIter = iterator;
6139 }
6140 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
6141 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
6142
6143 // perform the asType transforms under an exception transformer, as per spec.:
6144 try {
6145 startIter = startIter.asType(iteratorType);
6146 nextVal = nextRaw.asType(nextValType);
6147 } catch (WrongMethodTypeException ex) {
6148 throw new IllegalArgumentException(ex);
6149 }
6150 }
6151
6152 MethodHandle retv = null, step = body;
6153 if (returnType != void.class) {
6154 // the simple thing first: in (I V A...), drop the I to get V
6155 retv = dropArguments(identity(returnType), 0, Iterator.class);
6156 // body type signature (V T A...), internal loop types (I V A...)
6157 step = swapArguments(body, 0, 1); // swap V <-> T
6158 }
6159
6160 MethodHandle[]
6161 iterVar = { startIter, null, hasNext, retv },
6162 bodyClause = { init, filterArgument(step, 0, nextVal) };
6163 return loop(iterVar, bodyClause);
6164 }
6165
6166 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
6167 Objects.requireNonNull(body);
6168 MethodType bodyType = body.type();
6169 Class<?> returnType = bodyType.returnType();
6170 List<Class<?>> internalParamList = bodyType.parameterList();
6171 // strip leading V value if present
6172 int vsize = (returnType == void.class ? 0 : 1);
6173 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
6174 // argument list has no "V" => error
6175 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6176 throw misMatchedTypes("body function", bodyType, expected);
6177 } else if (internalParamList.size() <= vsize) {
6178 // missing T type => error
6179 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
6180 throw misMatchedTypes("body function", bodyType, expected);
6181 }
6182 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
6183 Class<?> iterableType = null;
6184 if (iterator != null) {
6185 // special case; if the body handle only declares V and T then
6186 // the external parameter list is obtained from iterator handle
6187 if (externalParamList.isEmpty()) {
6188 externalParamList = iterator.type().parameterList();
6189 }
6190 MethodType itype = iterator.type();
6191 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
6192 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
6193 }
6194 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
6195 MethodType expected = methodType(itype.returnType(), externalParamList);
6196 throw misMatchedTypes("iterator parameters", itype, expected);
6197 }
6198 } else {
6199 if (externalParamList.isEmpty()) {
6200 // special case; if the iterator handle is null and the body handle
6201 // only declares V and T then the external parameter list consists
6202 // of Iterable
6203 externalParamList = Arrays.asList(Iterable.class);
6204 iterableType = Iterable.class;
6205 } else {
6206 // special case; if the iterator handle is null and the external
6207 // parameter list is not empty then the first parameter must be
6208 // assignable to Iterable
6209 iterableType = externalParamList.get(0);
6210 if (!Iterable.class.isAssignableFrom(iterableType)) {
6211 throw newIllegalArgumentException(
6212 "inferred first loop argument must inherit from Iterable: " + iterableType);
6213 }
6214 }
6215 }
6216 if (init != null) {
6217 MethodType initType = init.type();
6218 if (initType.returnType() != returnType ||
6219 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
6220 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
6221 }
6222 }
6223 return iterableType; // help the caller a bit
6224 }
6225
6226 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
6227 // there should be a better way to uncross my wires
6228 int arity = mh.type().parameterCount();
6229 int[] order = new int[arity];
6230 for (int k = 0; k < arity; k++) order[k] = k;
6231 order[i] = j; order[j] = i;
6232 Class<?>[] types = mh.type().parameterArray();
6233 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
6234 MethodType swapType = methodType(mh.type().returnType(), types);
6235 return permuteArguments(mh, swapType, order);
6236 }
6237
6238 /**
6239 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
6240 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
6241 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
6242 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
6243 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
6244 * {@code try-finally} handle.
6245 * <p>
6246 * The {@code cleanup} handle will be passed one or two additional leading arguments.
6247 * The first is the exception thrown during the
6248 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
6249 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
6250 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
6251 * The second argument is not present if the {@code target} handle has a {@code void} return type.
6252 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
6253 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
6254 * <p>
6255 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
6256 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
6257 * two extra leading parameters:<ul>
6258 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
6259 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
6260 * the result from the execution of the {@code target} handle.
6261 * This parameter is not present if the {@code target} returns {@code void}.
6262 * </ul>
6263 * <p>
6264 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
6265 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
6266 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
6267 * the cleanup.
6268 * <blockquote><pre>{@code
6269 * V target(A..., B...);
6270 * V cleanup(Throwable, V, A...);
6271 * V adapter(A... a, B... b) {
6272 * V result = (zero value for V);
6273 * Throwable throwable = null;
6274 * try {
6275 * result = target(a..., b...);
6276 * } catch (Throwable t) {
6277 * throwable = t;
6278 * throw t;
6279 * } finally {
6280 * result = cleanup(throwable, result, a...);
6281 * }
6282 * return result;
6283 * }
6284 * }</pre></blockquote>
6285 * <p>
6286 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6287 * be modified by execution of the target, and so are passed unchanged
6288 * from the caller to the cleanup, if it is invoked.
6289 * <p>
6290 * The target and cleanup must return the same type, even if the cleanup
6291 * always throws.
6292 * To create such a throwing cleanup, compose the cleanup logic
6293 * with {@link #throwException throwException},
6294 * in order to create a method handle of the correct return type.
6295 * <p>
6296 * Note that {@code tryFinally} never converts exceptions into normal returns.
6297 * In rare cases where exceptions must be converted in that way, first wrap
6298 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
6299 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
6300 * <p>
6301 * It is recommended that the first parameter type of {@code cleanup} be
6302 * declared {@code Throwable} rather than a narrower subtype. This ensures
6303 * {@code cleanup} will always be invoked with whatever exception that
6304 * {@code target} throws. Declaring a narrower type may result in a
6305 * {@code ClassCastException} being thrown by the {@code try-finally}
6306 * handle if the type of the exception thrown by {@code target} is not
6307 * assignable to the first parameter type of {@code cleanup}. Note that
6308 * various exception types of {@code VirtualMachineError},
6309 * {@code LinkageError}, and {@code RuntimeException} can in principle be
6310 * thrown by almost any kind of Java code, and a finally clause that
6311 * catches (say) only {@code IOException} would mask any of the others
6312 * behind a {@code ClassCastException}.
6313 *
6314 * @param target the handle whose execution is to be wrapped in a {@code try} block.
6315 * @param cleanup the handle that is invoked in the finally block.
6316 *
6317 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
6318 * @throws NullPointerException if any argument is null
6319 * @throws IllegalArgumentException if {@code cleanup} does not accept
6320 * the required leading arguments, or if the method handle types do
6321 * not match in their return types and their
6322 * corresponding trailing parameters
6323 *
6324 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
6325 * @since 9
6326 */
6327 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
6328 List<Class<?>> targetParamTypes = target.type().parameterList();
6329 Class<?> rtype = target.type().returnType();
6330
6331 tryFinallyChecks(target, cleanup);
6332
6333 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
6334 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6335 // target parameter list.
6336 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
6337
6338 // Ensure that the intrinsic type checks the instance thrown by the
6339 // target against the first parameter of cleanup
6340 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
6341
6342 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
6343 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
6344 }
6345
6346 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
6347 Class<?> rtype = target.type().returnType();
6348 if (rtype != cleanup.type().returnType()) {
6349 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
6350 }
6351 MethodType cleanupType = cleanup.type();
6352 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
6353 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
6354 }
6355 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
6356 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
6357 }
6358 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
6359 // target parameter list.
6360 int cleanupArgIndex = rtype == void.class ? 1 : 2;
6361 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
6362 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
6363 cleanup.type(), target.type());
6364 }
6365 }
6366
6367 }